Fix typo.

Add a way to cache result for future evaluations.
Add a session independent cache.
2009-07-08 09:44:22 +00:00 · 2009-07-08 09:27:35 +00:00 · 2009-07-08 09:26:15 +00:00 · 2009-07-08 09:18:26 +00:00
179 changed files with 5872 additions and 4913 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -1,262 +0,0 @@
-# START "git svn show-ignore"
-
-# /
-/Makefile
-/Makefile.in
-/aclocal.m4
-/autom4te.cache
-/config.*
-/configure
-/nix.spec
-/stamp-h1
-/svn-revision
-/NEWS
-/libtool
-
-# /config/
-/config/config.guess
-/config/config.sub
-/config/depcomp
-/config/install-sh
-/config/missing
-/config/mkinstalldirs
-/config/ltmain.sh
-
-# /corepkgs/
-/corepkgs/Makefile
-/corepkgs/Makefile.in
-
-# /corepkgs/buildenv/
-/corepkgs/buildenv/Makefile.in
-/corepkgs/buildenv/Makefile
-/corepkgs/buildenv/builder.pl
-
-# /corepkgs/channels/
-/corepkgs/channels/Makefile.in
-/corepkgs/channels/Makefile
-/corepkgs/channels/unpack.sh
-
-# /corepkgs/nar/
-/corepkgs/nar/Makefile
-/corepkgs/nar/Makefile.in
-/corepkgs/nar/nar.sh
-/corepkgs/nar/unnar.sh
-
-# /doc/
-/doc/Makefile
-/doc/Makefile.in
-
-# /doc/manual/
-/doc/manual/Makefile
-/doc/manual/Makefile.in
-/doc/manual/manual.html
-/doc/manual/manual.is-valid
-/doc/manual/*.1
-/doc/manual/*.8
-/doc/manual/images
-/doc/manual/version.txt
-/doc/manual/NEWS.html
-/doc/manual/NEWS.txt
-
-# /externals/
-/externals/Makefile
-/externals/Makefile.in
-/externals/aterm-*
-/externals/have-aterm
-/externals/build-aterm
-/externals/inst-aterm
-/externals/bzip2-*
-/externals/have-bzip2
-/externals/build-bzip2
-/externals/inst-bzip2
-
-# /make/examples/aterm/
-/make/examples/aterm/result*
-
-# /make/examples/aterm/aterm/
-/make/examples/aterm/aterm/*
-
-# /make/examples/aterm/test/
-/make/examples/aterm/test/*
-
-# /misc/
-/misc/Makefile.in
-/misc/Makefile
-
-# /misc/emacs/
-/misc/emacs/Makefile.in
-/misc/emacs/Makefile
-
-# /scripts/
-/scripts/Makefile
-/scripts/Makefile.in
-/scripts/nix-profile.sh
-/scripts/nix-pull
-/scripts/nix-push
-/scripts/nix-switch
-/scripts/nix-collect-garbage
-/scripts/nix-prefetch-url
-/scripts/nix-install-package
-/scripts/nix-channel
-/scripts/nix-build
-/scripts/nix-copy-closure
-/scripts/readmanifest.pm
-/scripts/readconfig.pm
-/scripts/download-using-manifests.pl
-/scripts/copy-from-other-stores.pl
-/scripts/generate-patches.pl
-/scripts/find-runtime-roots.pl
-/scripts/build-remote.pl
-
-# /src/
-/src/Makefile
-/src/Makefile.in
-
-# /src/bin2c/
-/src/bin2c/Makefile.in
-/src/bin2c/Makefile
-/src/bin2c/bin2c
-/src/bin2c/.deps
-/src/bin2c/.libs
-
-# /src/boost/
-/src/boost/Makefile
-/src/boost/Makefile.in
-
-# /src/boost/format/
-/src/boost/format/Makefile
-/src/boost/format/Makefile.in
-/src/boost/format/.deps
-/src/boost/format/libformat.a
-/src/boost/format/.libs
-
-# /src/bsdiff-4.3/
-/src/bsdiff-4.3/Makefile
-/src/bsdiff-4.3/Makefile.in
-/src/bsdiff-4.3/bsdiff
-/src/bsdiff-4.3/bspatch
-/src/bsdiff-4.3/.deps
-/src/bsdiff-4.3/.libs
-
-# /src/libexpr/
-/src/libexpr/Makefile
-/src/libexpr/Makefile.in
-/src/libexpr/.deps
-/src/libexpr/libexpr.a
-/src/libexpr/lexer-tab.cc
-/src/libexpr/lexer-tab.hh
-/src/libexpr/parser-tab.cc
-/src/libexpr/parser-tab.hh
-/src/libexpr/parser-tab.output
-/src/libexpr/nixexpr-ast.hh
-/src/libexpr/nixexpr-ast.cc
-/src/libexpr/.libs
-/src/libexpr/nix.tbl
-
-# /src/libmain/
-/src/libmain/Makefile
-/src/libmain/Makefile.in
-/src/libmain/.deps
-/src/libmain/libmain.a
-/src/libmain/.libs
-
-# /src/libstore/
-/src/libstore/Makefile
-/src/libstore/Makefile.in
-/src/libstore/.deps
-/src/libstore/libstore.a
-/src/libstore/derivations-ast.cc
-/src/libstore/derivations-ast.hh
-/src/libstore/.libs
-
-# /src/libutil/
-/src/libutil/Makefile
-/src/libutil/Makefile.in
-/src/libutil/.deps
-/src/libutil/libutil.a
-/src/libutil/.libs
-
-# /src/nix-env/
-/src/nix-env/Makefile.in
-/src/nix-env/Makefile
-/src/nix-env/.deps
-/src/nix-env/nix-env
-/src/nix-env/help.txt.hh
-/src/nix-env/.libs
-
-# /src/nix-hash/
-/src/nix-hash/Makefile
-/src/nix-hash/Makefile.in
-/src/nix-hash/.deps
-/src/nix-hash/.libs
-/src/nix-hash/nix-hash
-/src/nix-hash/help.txt.hh
-
-# /src/nix-instantiate/
-/src/nix-instantiate/Makefile.in
-/src/nix-instantiate/Makefile
-/src/nix-instantiate/.deps
-/src/nix-instantiate/nix-instantiate
-/src/nix-instantiate/help.txt.hh
-/src/nix-instantiate/.libs
-
-# /src/nix-log2xml/
-/src/nix-log2xml/Makefile.in
-/src/nix-log2xml/Makefile
-/src/nix-log2xml/.deps
-/src/nix-log2xml/nix-log2xml
-/src/nix-log2xml/test*.*
-/src/nix-log2xml/.libs
-/src/nix-log2xml/*.log
-/src/nix-log2xml/*.xml
-/src/nix-log2xml/*.html
-
-# /src/nix-setuid-helper/
-/src/nix-setuid-helper/Makefile.in
-/src/nix-setuid-helper/Makefile
-/src/nix-setuid-helper/.deps
-/src/nix-setuid-helper/nix-setuid-helper
-/src/nix-setuid-helper/help.txt.hh
-/src/nix-setuid-helper/.libs
-
-# /src/nix-store/
-/src/nix-store/Makefile
-/src/nix-store/Makefile.in
-/src/nix-store/.deps
-/src/nix-store/help.txt.hh
-/src/nix-store/nix-store
-/src/nix-store/.libs
-
-# /src/nix-worker/
-/src/nix-worker/Makefile.in
-/src/nix-worker/Makefile
-/src/nix-worker/.deps
-/src/nix-worker/nix-worker
-/src/nix-worker/help.txt.hh
-/src/nix-worker/.libs
-
-# /tests/
-/tests/Makefile
-/tests/Makefile.in
-/tests/test-tmp
-/tests/config.nix
-/tests/common.sh
-/tests/dummy
-
-# /tests/lang/
-/tests/lang/*.out
-/tests/lang/*.out.xml
-/tests/lang/*.ast
-
-# END "git svn show-ignore"
-
-*.lo
-*.la
-*.o
-*~
-
-# GNU Global
-GPATH
-GRTAGS
-GSYMS
-GTAGS
--- a/Makefile.am
+++ b/Makefile.am
@@ -29,9 +29,11 @@ init-state:
 	$(INSTALL) $(INIT_FLAGS) -d $(DESTDIR)$(localstatedir)/nix/profiles
 	$(INSTALL) $(INIT_FLAGS) -d $(DESTDIR)$(localstatedir)/nix/gcroots
 	$(INSTALL) $(INIT_FLAGS) -d $(DESTDIR)$(localstatedir)/nix/temproots
+	$(INSTALL) $(INIT_FLAGS) $(GROUP_WRITABLE) -d $(DESTDIR)$(localstatedir)/nix/gcroots/tmp
+	$(INSTALL) $(INIT_FLAGS) $(GROUP_WRITABLE) -d $(DESTDIR)$(localstatedir)/nix/gcroots/channels
 	ln -sfn $(localstatedir)/nix/profiles $(DESTDIR)$(localstatedir)/nix/gcroots/profiles
 	$(INSTALL) $(INIT_FLAGS) -d $(DESTDIR)$(localstatedir)/nix/userpool
-	-$(INSTALL) $(INIT_FLAGS) -m 1777 -d $(DESTDIR)$(storedir)
+	$(INSTALL) $(INIT_FLAGS) -m 1777 -d $(DESTDIR)$(storedir)
 	$(INSTALL) $(INIT_FLAGS) $(GROUP_WRITABLE) -d $(DESTDIR)$(localstatedir)/nix/manifests
 	ln -sfn $(localstatedir)/nix/manifests $(DESTDIR)$(localstatedir)/nix/gcroots/manifests

--- a/configure.ac
+++ b/configure.ac
@@ -55,7 +55,7 @@ test "$localstatedir" = '${prefix}/var' && localstatedir=/nix/var
 # except that it requires the ATerm "lib" directory to be in $PATH, as
 # Windows doesn't have anything like an RPATH embedded in executable.
 # Since this is kind of annoying, we use static libraries for now.
-
+    
 AC_ARG_ENABLE(static-nix, AC_HELP_STRING([--enable-static-nix],
  [produce statically linked binaries]),
  static_nix=$enableval, static_nix=no)
@@ -63,38 +63,23 @@ AC_ARG_ENABLE(static-nix, AC_HELP_STRING([--enable-static-nix],
 if test "$sys_name" = cygwin; then
   static_nix=yes
 fi
-
+  
 if test "$static_nix" = yes; then
    AC_DISABLE_SHARED
    AC_ENABLE_STATIC
 fi

-
+  
 # Windows-specific stuff.
 if test "$sys_name" = "cygwin"; then
    # We cannot delete open files.
    AC_DEFINE(CANNOT_DELETE_OPEN_FILES, 1, [Whether it is impossible to delete open files.])
 fi

-# Solaris-specific stuff.
-if test "$sys_name" = "sunos"; then
-    # Solaris requires -lsocket -lnsl for network functions
-    ADDITIONAL_NETWORK_LIBS="-lsocket -lnsl"
-    AC_SUBST(ADDITIONAL_NETWORK_LIBS)
-fi

 AC_PROG_CC
 AC_PROG_CXX

-# To build programs to be run in the build machine
-if test "$CC_FOR_BUILD" = ""; then
-    if test "$cross_compiling" = "yes"; then
-        AC_CHECK_PROGS(CC_FOR_BUILD, gcc cc)
-    else
-        CC_FOR_BUILD="$CC"
-    fi
-fi
-AC_SUBST([CC_FOR_BUILD])

 # We are going to use libtool.
 AC_DISABLE_STATIC
@@ -103,7 +88,8 @@ AC_PROG_LIBTOOL


 # Use 64-bit file system calls so that we can support files > 2 GiB.
-AC_SYS_LARGEFILE
+CFLAGS="-D_FILE_OFFSET_BITS=64 $CFLAGS"
+CXXFLAGS="-D_FILE_OFFSET_BITS=64 $CXXFLAGS"


 # Check for pubsetbuf.
@@ -154,11 +140,11 @@ NEED_PROG(bash, bash)
 NEED_PROG(patch, patch)
 AC_PATH_PROG(xmllint, xmllint, false)
 AC_PATH_PROG(xsltproc, xsltproc, false)
+AC_PATH_PROG(jing, jing, false) # needed because xmllint --relaxng seems broken
 AC_PATH_PROG(w3m, w3m, false)
 AC_PATH_PROG(flex, flex, false)
 AC_PATH_PROG(bison, bison, false)
 NEED_PROG(perl, perl)
-NEED_PROG(sed, sed)
 NEED_PROG(tar, tar)
 AC_PATH_PROG(dot, dot)
 AC_PATH_PROG(dblatex, dblatex)
@@ -203,6 +189,48 @@ AC_ARG_WITH(store-dir, AC_HELP_STRING([--with-store-dir=PATH],
  storedir=$withval, storedir='/nix/store')
 AC_SUBST(storedir)

+AC_ARG_ENABLE(old-db-compat, AC_HELP_STRING([--disable-old-db-compat],
+  [disable support for converting from old Berkeley DB-based Nix stores]),
+  old_db_compat=$enableval, old_db_compat=yes)
+AM_CONDITIONAL(OLD_DB_COMPAT, test "$old_db_compat" = "yes")
+
+AC_ARG_WITH(bdb, AC_HELP_STRING([--with-bdb=PATH],
+  [prefix of Berkeley DB (for Nix <= 0.11 compatibility)]),
+  bdb=$withval, bdb=)
+AM_CONDITIONAL(HAVE_BDB, test -n "$bdb")
+if test -z "$bdb"; then
+  bdb_lib='-L${top_builddir}/externals/inst-bdb/lib -ldb_cxx'
+  bdb_include='-I${top_builddir}/externals/inst-bdb/include'
+else
+  bdb_lib="-L$bdb/lib -ldb_cxx"
+  bdb_include="-I$bdb/include"
+fi
+if test "$old_db_compat" = "no"; then
+  bdb_lib=
+  bdb_include=
+else
+  AC_DEFINE(OLD_DB_COMPAT, 1, [Whether to support converting from old Berkeley DB-based Nix stores.])
+fi
+AC_SUBST(bdb_lib)
+AC_SUBST(bdb_include)
+
+AC_ARG_WITH(aterm, AC_HELP_STRING([--with-aterm=PATH],
+  [prefix of CWI ATerm library]),
+  aterm=$withval, aterm=)
+AM_CONDITIONAL(HAVE_ATERM, test -n "$aterm")
+if test -z "$aterm"; then
+  aterm_lib='-L${top_builddir}/externals/inst-aterm/lib -lATerm'
+  aterm_include='-I${top_builddir}/externals/inst-aterm/include'
+  aterm_bin='${top_builddir}/externals/inst-aterm/bin'
+else
+  aterm_lib="-L$aterm/lib -lATerm"
+  aterm_include="-I$aterm/include"
+  aterm_bin="$aterm/bin"
+fi
+AC_SUBST(aterm_lib)
+AC_SUBST(aterm_include)
+AC_SUBST(aterm_bin)
+
 AC_ARG_WITH(openssl, AC_HELP_STRING([--with-openssl=PATH],
  [prefix of the OpenSSL library]),
  openssl=$withval, openssl=)
@@ -232,7 +260,7 @@ else
  bzip2_include="-I$bzip2/include"
  bzip2_bin="$bzip2/bin"
  bzip2_bin_test="$bzip2/bin"
-fi
+fi   
 AC_SUBST(bzip2_lib)
 AC_SUBST(bzip2_include)
 AC_SUBST(bzip2_bin)
@@ -257,7 +285,7 @@ AC_CHECK_FUNCS([strsignal])
 AC_CHECK_FUNCS([posix_fallocate])


-# This is needed if ATerm or bzip2 are static libraries,
+# This is needed if ATerm, Berkeley DB or bzip2 are static libraries,
 # and the Nix libraries are dynamic.
 if test "$(uname)" = "Darwin"; then
    LDFLAGS="-all_load $LDFLAGS"
--- a/corepkgs/buildenv/builder.pl.in
+++ b/corepkgs/buildenv/builder.pl.in
@@ -29,18 +29,10 @@ sub createLinks {
        $baseName =~ s/^.*\///g; # strip directory
        my $dstFile = "$dstDir/$baseName";

-        # The files below are special-cased so that they don't show up
-        # in user profiles, either because they are useless, or
-        # because they would cause pointless collisions (e.g., each
-        # Python package brings its own
-        # `$out/lib/pythonX.Y/site-packages/easy-install.pth'.)
        # Urgh, hacky...
-        if ($srcFile =~ /\/propagated-build-inputs$/ ||
+	if ($srcFile =~ /\/propagated-build-inputs$/ ||
            $srcFile =~ /\/nix-support$/ ||
            $srcFile =~ /\/perllocal.pod$/ ||
-            $srcFile =~ /\/easy-install.pth$/ ||
-            $srcFile =~ /\/site.py$/ ||
-            $srcFile =~ /\/site.pyc$/ ||
            $srcFile =~ /\/info\/dir$/ ||
            $srcFile =~ /\/log$/)
        {
@@ -168,4 +160,4 @@ while (scalar(keys %postponed) > 0) {
 print STDERR "created $symlinks symlinks in user environment\n";


-symlink($ENV{"manifest"}, "$out/manifest.nix") or die "cannot create manifest";
+symlink($ENV{"manifest"}, "$out/manifest") or die "cannot create manifest";
--- a/corepkgs/channels/unpack.sh.in
+++ b/corepkgs/channels/unpack.sh.in
@@ -1,8 +1,5 @@
 #! @shell@ -e

-# Cygwin compatibility hack: bunzip2 expects cygwin.dll in $PATH.
-export PATH=@coreutils@
-
@coreutils@/mkdir $out
@coreutils@/mkdir $out/tmp
 cd $out/tmp
--- a/doc/manual/Makefile.am
+++ b/doc/manual/Makefile.am
@@ -6,12 +6,7 @@ XSLTPROC = $(xsltproc) $(xmlflags) \
 --param xref.with.number.and.title 1 \
 --param toc.section.depth 3 \
 --param admon.style \'\' \
- --param callout.graphics.extension \'.gif\' \
- --param contrib.inline.enabled 0
-
-dblatex_opts = \
- -P doc.collab.show=0 \
- -P latex.output.revhistory=0
+ --param callout.graphics.extension \'.gif\'

 # Note: we use GIF for now, since the PNGs shipped with Docbook aren't
 # transparent.
@@ -34,9 +29,13 @@ MANUAL_SRCS = manual.xml introduction.xml installation.xml \
 conf-file.xml release-notes.xml \
 style.css images

-# Note: RelaxNG validation requires xmllint >= 2.7.4.
 manual.is-valid: $(MANUAL_SRCS) version.txt
-	$(XMLLINT) --noout --nonet --xinclude --noxincludenode --relaxng $(docbookrng)/docbook.rng $<
+#	$(XMLLINT) --xinclude $< | $(XMLLINT) --noout --nonet --relaxng $(docbookrng)/docbook.rng -
+	if test "$(jing)" != "false"; then \
+		$(XMLLINT) --xinclude $< | $(jing) $(docbookrng)/docbook.rng /dev/fd/0; \
+	else \
+		echo "Not validating."; \
+	fi
 	touch $@

 version.txt:
@@ -51,7 +50,7 @@ manual.html: $(MANUAL_SRCS) manual.is-valid images

 manual.pdf: $(MANUAL_SRCS) manual.is-valid images
 	if test "$(dblatex)" != ""; then \
-		$(dblatex) $(dblatex_opts) manual.xml; \
+		$(dblatex) manual.xml; \
 	else \
 		echo "Please install dblatex and rerun configure."; \
 		exit 1; \
--- a/doc/manual/builtins.xml
+++ b/doc/manual/builtins.xml
@@ -324,16 +324,6 @@ x: x + 456</programlisting>
  </varlistentry>

  
-  <varlistentry><term><function>builtins.intersectAttrs</function>
-  <replaceable>e1</replaceable> <replaceable>e2</replaceable></term>
-
-    <listitem><para>Return an attribute set consisting of the
-    attributes in the set <replaceable>e2</replaceable> that also
-    exist in the set <replaceable>e1</replaceable>.</para></listitem>
-
-  </varlistentry>
-        
-    
  <varlistentry><term><function>builtins.isAttrs</function>
  <replaceable>e</replaceable></term>

--- a/doc/manual/conf-file.xml
+++ b/doc/manual/conf-file.xml
@@ -233,17 +233,7 @@ build-use-chroot = /dev /proc /bin</programlisting>
    <filename>configure</filename> at build time.</para></listitem>

  </varlistentry>
-
-
-  <varlistentry><term><literal>fsync-metadata</literal></term>
-
-    <listitem><para>If set to <literal>true</literal>, changes to the
-    Nix store metadata (in <filename>/nix/var/nix/db</filename>) are
-    synchronously flushed to disk.  This improves robustness in case
-    of system crashes, but reduces performance.  The default is
-    <literal>false</literal>.</para></listitem>
-
-  </varlistentry>
+  
    
 </variablelist>

--- a/doc/manual/installation.xml
+++ b/doc/manual/installation.xml
@@ -96,15 +96,24 @@ ubiquitous 2.5.4a won't.  Note that these are only required if you
 modify the parser or when you are building from the Subversion
 repository.</para>

-<para>Nix uses the bzip2 compressor (including the bzip2 library).  It
-is included in the Nix source distribution.  If you build from the
-Subversion repository, you must download it yourself and place it in
-the <filename>externals/</filename> directory.  See
+<para>Nix uses CWI's ATerm library and the bzip2 compressor (including
+the bzip2 library).  These are included in the Nix source
+distribution.  If you build from the Subversion repository, you must
+download them yourself and place them in the
+<filename>externals/</filename> directory.  See
 <filename>externals/Makefile.am</filename> for the precise URLs of
-this packages.  Alternatively, if you already have it installed, you
-can use <command>configure</command>'s <option>--with-bzip2</option>
+these packages.  Alternatively, if you already have them installed,
+you can use <command>configure</command>'s
+<option>--with-aterm</option> and <option>--with-bzip2</option>
 options to point to their respective locations.</para>

+<para>If you want to be able to upgrade Nix stores from before version
+0.12pre12020, you need Sleepycat's Berkeley DB version version 4.5.
+(Other versions may not have compatible database formats.).  Berkeley
+DB 4.5 is included in the Nix source distribution.  If you do not need
+this ability, you can build Nix with the
+<option>--disable-old-db-compat</option> configure option.</para>
+
 </section>


@@ -124,32 +133,23 @@ $ make install</screen>
 preceded by the command:

 <screen>
-$ ./bootstrap.sh</screen>
+$ ./bootstrap</screen>

 </para>

 <para>The installation path can be specified by passing the
 <option>--prefix=<replaceable>prefix</replaceable></option> to
 <command>configure</command>.  The default installation directory is
-<filename>/usr/local</filename>.  You can change this to any location
-you like.  You must have write permission to the
+<filename>/nix</filename>.  You can change this to any location you
+like.  You must have write permission to the
 <replaceable>prefix</replaceable> path.</para>

-<para>Nix keeps its <emphasis>store</emphasis> (the place where
-packages are stored) in <filename>/nix/store</filename> by default.
-This can be changed using
-<option>--with-store-dir=<replaceable>path</replaceable></option>.</para>
+<warning><para>It is best <emphasis>not</emphasis> to change the
+installation prefix from its default, since doing so makes it
+impossible to use pre-built binaries from the standard Nixpkgs
+channels.</para></warning>

-<warning><para>It is best <emphasis>not</emphasis> to change the Nix
-store from its default, since doing so makes it impossible to use
-pre-built binaries from the standard Nixpkgs channels — that is, all
-packages will need to be built from source.</para></warning>
-
-<para>Nix keeps state (such as its database and log files) in
-<filename>/nix/var</filename> by default.  This can be changed using
-<option>--localstatedir=<replaceable>path</replaceable></option>.</para>
-
-<para>If you want to rebuild the documentation, pass the full path to
+<para>If you want to rebuilt the documentation, pass the full path to
 the DocBook RELAX NG schemas and to the DocBook XSL stylesheets using
 the
 <option>--with-docbook-rng=<replaceable>path</replaceable></option>
@@ -160,26 +160,27 @@ options.</para>
 </section>


-<section><title>Installing a binary distribution</title>
+<section><title>Installing from RPMs</title>

-<para>RPM and Deb packages of Nix for a number of different versions
-of Fedora, openSUSE, Debian and Ubuntu can be downloaded from <link
-xlink:href="http://nixos.org/" />.  Once downloaded, the RPMs can be
-installed or upgraded using <command>rpm -U</command>.  For example,
+<para>RPM packages of Nix can be downloaded from <link
+xlink:href="http://nixos.org/" />.  These RPMs should work for most
+fairly recent releases of SuSE and Red Hat Linux.  They have been
+known to work work on SuSE Linux 8.1 and 9.0, and Red Hat 9.0.  In
+fact, it should work on any RPM-based Linux distribution based on
+<literal>glibc</literal> 2.3 or later.</para>
+
+<para>Once downloaded, the RPMs can be installed or upgraded using
+<command>rpm -U</command>.  For example,

 <screen>
-$ rpm -U nix-0.13pre18104-1.i386.rpm</screen>
-
-Likewise, for a Deb package:
-
-<screen>
-$ dpkg -i nix_0.13pre18104-1_amd64.deb</screen>
+$ rpm -U nix-0.5pre664-1.i386.rpm</screen>

 </para>

-<para>Nix can be uninstalled using <command>rpm -e nix</command> or
-<command>dpkg -r nix</command>.  After this you should manually remove
-the Nix store and other auxiliary data, if desired:
+<para>The RPMs install into the directory <filename>/nix</filename>.
+Nix can be uninstalled using <command>rpm -e nix</command>.  After
+this it will be necessary to manually remove the Nix store and other
+auxiliary data:

 <screen>
 $ rm -rf /nix/store
@@ -190,7 +191,6 @@ $ rm -rf /nix/var</screen>
 </section>


-<!-- TODO: should be updated
 <section><title>Upgrading Nix through Nix</title>

 <para>You can install the latest stable version of Nix through Nix
@@ -203,7 +203,6 @@ installation</link> by clicking on the package links at <link
 xlink:href="http://nixos.org/releases/full-index-nix.html" />.</para>

 </section>
-->


 <section><title>Security</title>
--- a/doc/manual/introduction.xml
+++ b/doc/manual/introduction.xml
@@ -320,7 +320,7 @@ overview of NixOS is given in the HotOS XI paper <citetitle
 xlink:href="http://www.st.ewi.tudelft.nl/~dolstra/pubs/hotos-final.pdf">Purely
 Functional System Configuration Management</citetitle>.  The Nix
 homepage has <link
-xlink:href="http://nixos.org/docs/papers.html">an up-to-date list
+xlink:href="http://nix.cs.uu.nl/docs/papers.html">an up-to-date list
 of Nix-related papers</link>.</para>

 <para>Nix is the subject of Eelco Dolstra’s PhD thesis <citetitle
--- a/doc/manual/manual.xml
+++ b/doc/manual/manual.xml
@@ -17,7 +17,6 @@
        <orgname>Delft University of Technology</orgname>
        <orgdiv>Department of Software Technology</orgdiv>
      </affiliation>
-      <contrib>Author</contrib>
    </author>

    <copyright>
@@ -26,11 +25,10 @@
      <year>2006</year>
      <year>2007</year>
      <year>2008</year>
-      <year>2009</year>
      <holder>Eelco Dolstra</holder>
    </copyright>

-    <date>September 2009</date>
+    <date>November 2008</date>
    
  </info>

@@ -51,25 +49,64 @@
    
    <section>
      <title>Main commands</title>
-      <xi:include href="nix-env.xml" />
-      <xi:include href="nix-instantiate.xml" />
-      <xi:include href="nix-store.xml" />
+      <section xml:id="sec-nix-env">
+        <title>nix-env</title>
+        <xi:include href="nix-env.xml" />
+      </section>
+      <section xml:id="sec-nix-instantiate">
+        <title>nix-instantiate</title>
+        <xi:include href="nix-instantiate.xml" />
+      </section>
+      <section xml:id="sec-nix-store">
+        <title>nix-store</title>
+        <xi:include href="nix-store.xml" />
+      </section>
    </section>
    
    <section>
      <title>Utilities</title>
-      <xi:include href="nix-build.xml" />
-      <xi:include href="nix-channel.xml" />
-      <xi:include href="nix-collect-garbage.xml" />
-      <xi:include href="nix-copy-closure.xml" />
-      <xi:include href="nix-hash.xml" />
-      <xi:include href="nix-install-package.xml" />
-      <xi:include href="nix-prefetch-url.xml" />
-      <xi:include href="nix-pull.xml" />
-      <xi:include href="nix-push.xml" />
-      <xi:include href="nix-worker.xml" />
+      <section xml:id="sec-nix-build">
+        <title>nix-build</title>
+        <xi:include href="nix-build.xml" />
+      </section>
+      <section xml:id="sec-nix-channel">
+        <title>nix-channel</title>
+        <xi:include href="nix-channel.xml" />
+      </section>
+      <section xml:id="sec-nix-collect-garbage">
+        <title>nix-collect-garbage</title>
+        <xi:include href="nix-collect-garbage.xml" />
+      </section>
+      <section xml:id="sec-nix-copy-closure">
+        <title>nix-copy-closure</title>
+        <xi:include href="nix-copy-closure.xml" />
+      </section>
+      <section xml:id="sec-nix-hash">
+        <title>nix-hash</title>
+        <xi:include href="nix-hash.xml" />
+      </section>
+      <section xml:id="sec-nix-install-package">
+        <title>nix-install-package</title>
+        <xi:include href="nix-install-package.xml" />
+      </section>
+      <section xml:id="sec-nix-prefetch-url">
+        <title>nix-prefetch-url</title>
+        <xi:include href="nix-prefetch-url.xml" />
+      </section>
+      <section xml:id="sec-nix-pull">
+        <title>nix-pull</title>
+        <xi:include href="nix-pull.xml" />
+      </section>
+      <section xml:id="sec-nix-push">
+        <title>nix-push</title>
+        <xi:include href="nix-push.xml" />
+      </section>
+      <section xml:id="sec-nix-worker">
+        <title>nix-worker</title>
+        <xi:include href="nix-worker.xml" />
+      </section>
    </section>
-
+    
  </appendix>

  <xi:include href="troubleshooting.xml" />
--- a/doc/manual/nix-build.xml
+++ b/doc/manual/nix-build.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-build">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-build</refentrytitle>
--- a/doc/manual/nix-channel.xml
+++ b/doc/manual/nix-channel.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-channel">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-channel</refentrytitle>
--- a/doc/manual/nix-collect-garbage.xml
+++ b/doc/manual/nix-collect-garbage.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-collect-garbage">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-collect-garbage</refentrytitle>
--- a/doc/manual/nix-copy-closure.xml
+++ b/doc/manual/nix-copy-closure.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-copy-closure">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-copy-closure</refentrytitle>
--- a/doc/manual/nix-env.xml
+++ b/doc/manual/nix-env.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-env">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-env</refentrytitle>
--- a/doc/manual/nix-hash.xml
+++ b/doc/manual/nix-hash.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-hash">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-hash</refentrytitle>
--- a/doc/manual/nix-install-package.xml
+++ b/doc/manual/nix-install-package.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-install-package">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-install-package</refentrytitle>
--- a/doc/manual/nix-instantiate.xml
+++ b/doc/manual/nix-instantiate.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-instantiate">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-instantiate</refentrytitle>
--- a/doc/manual/nix-lang-ref.xml
+++ b/doc/manual/nix-lang-ref.xml
@@ -178,5 +178,100 @@
    </productionset>
    
  </sect1>
+  
+
+
+  <sect1>
+    <title>Semantics</title>
+
+
+    
+    <sect2>
+      <title>Built-in functions</title>
+
+      <para>
+        The Nix language provides the following built-in function
+        (<quote>primops</quote>):
+      </para>
+
+      <variablelist>
+
+        <varlistentry>
+          <term><function>import</function>
+          <replaceable>e</replaceable></term>
+          <listitem>
+            <para>
+              Evaluates the expression <replaceable>e</replaceable>,
+              which must yield a path value.  The Nix expression
+              stored at this path in the file system is then read,
+              parsed, and evaluated.  Returns the result of the
+              evaluation of the Nix expression just read.
+            </para>
+
+            <para>
+              Example: <literal>import ./foo.nix</literal> evaluates
+              the expression stored in <filename>foo.nix</filename>
+              (in the directory containing the expression in which the
+              <function>import</function> occurs).
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><function>derivation</function>
+          <replaceable>e</replaceable></term>
+          <listitem>
+            <para>
+              Evaluates the expression <replaceable>e</replaceable>,
+              which must yield an attribute set.  [...]
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><function>baseNameOf</function>
+          <replaceable>e</replaceable></term>
+          <listitem>
+            <para>
+              Evaluates the expression <replaceable>e</replaceable>,
+              which must yield a string value, and returns a string
+              representing its <emphasis>base name</emphasis>.  This
+              is the substring following the last path separator
+              (<literal>/</literal>).
+            </para>
+
+            <para>
+              Example: <literal>baseNameOf "/foo/bar"</literal>
+              returns <literal>"bar"</literal>, and
+              <literal>baseNameOf "/foo/bar/"</literal> returns
+              <literal>""</literal>.
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><function>toString</function>
+          <replaceable>e</replaceable></term>
+          <listitem>
+            <para>
+              Evaluates the expression <replaceable>e</replaceable>
+              and coerces it into a string, if possible.  Only
+              strings, paths, and URIs can be so coerced.
+            </para>
+
+            <para>
+              Example: <literal>toString
+              http://www.cs.uu.nl/</literal> returns
+              <literal>"http://www.cs.uu.nl/"</literal>.
+            </para>
+          </listitem>
+        </varlistentry>
+            
+      </variablelist>
+
+    </sect2>
+
+  </sect1>
+  

 </appendix>
--- a/doc/manual/nix-prefetch-url.xml
+++ b/doc/manual/nix-prefetch-url.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-prefetch-url">
+          xmlns:xi="http://www.w3.org/2001/XInclude">
  
 <refmeta>
  <refentrytitle>nix-prefetch-url</refentrytitle>
--- a/doc/manual/nix-pull.xml
+++ b/doc/manual/nix-pull.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-pull">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-pull</refentrytitle>
--- a/doc/manual/nix-push.xml
+++ b/doc/manual/nix-push.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-push">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-push</refentrytitle>
--- a/doc/manual/nix-store.xml
+++ b/doc/manual/nix-store.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-store">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-store</refentrytitle>
@@ -213,6 +212,8 @@ linkend="sec-nix-build"><command>nix-build</command></link> does.</para>
  </group>
  <arg><option>--max-freed</option> <replaceable>bytes</replaceable></arg>
  <arg><option>--max-links</option> <replaceable>nrlinks</replaceable></arg>
+  <arg><option>--max-atime</option> <replaceable>atime</replaceable></arg>
+  <arg><option>--use-atime</option></arg>
 </cmdsynopsis>

 </refsection>
@@ -290,6 +291,42 @@ options control what gets deleted and in what order:
    
  </varlistentry>

+  <varlistentry><term><option>--max-atime</option> <replaceable>atime</replaceable></term>
+  
+    <listitem><para>Only delete a store path if its last-accessed time
+    is less than <replaceable>atime</replaceable>.  This allows you to
+    garbage-collect only packages that haven’t been used recently.
+    The time is expressed as the number of seconds in the Unix epoch,
+    i.e., since 1970-01-01 00:00:00 UTC.  An easy way to convert to
+    this format is <literal>date +%s -d "<replaceable>date
+    specification</replaceable>"</literal>.</para>
+
+    <para>For directories, the last-accessed time is the highest
+    last-accessed time of any regular file in the directory (or in any
+    of its subdirectories).  That is, the <literal>atime</literal>
+    field maintained by the filesystem is ignored for directories.
+    This is because operations such as rebuilding the
+    <command>locate</command> database tend to update the
+    <literal>atime</literal> values of all directories, so they’re not
+    a useful indicator of whether a package was recently used.</para>
+
+    <para>Note that <command>nix-store --optimise</command> reads all
+    regular files in the Nix store, and so causes all last-accessed
+    times to be set to the present time.  This makes
+    <option>--max-atime</option> ineffective (for a while at
+    least).</para></listitem>
+    
+  </varlistentry>
+
+  <varlistentry><term><option>--use-atime</option></term>
+
+    <listitem><para>Delete store paths in order of ascending
+    last-accessed time.  This is useful in conjunction with the other
+    options to delete only the least recently used
+    packages.</para></listitem>
+
+  </varlistentry>
+  
 </variablelist>

 </para>
@@ -320,6 +357,13 @@ deleting `/nix/store/kq82idx6g0nyzsp2s14gfsc38npai7lf-cairo-1.0.4.tar.gz.drv'

 </para>

+<para>To delete unreachable paths not accessed in the last two months:
+
+<screen>
+$ nix-store --gc -v --max-atime $(date +%s -d "2 months ago")</screen>
+
+</para>
+
 <para>To delete at least 100 MiBs of unreachable paths:

 <screen>
@@ -342,7 +386,7 @@ $ nix-store --gc --max-freed $((100 * 1024 * 1024))</screen>

 <cmdsynopsis>
  <command>nix-store</command>
-  <arg choice='plain'><option>--delete</option></arg>
+  <arg choice='plain'><option>--gc</option></arg>
  <arg><option>--ignore-liveness</option></arg>
  <arg choice='plain' rep='repeat'><replaceable>paths</replaceable></arg>
 </cmdsynopsis>
@@ -404,7 +448,6 @@ error: cannot delete path `/nix/store/zq0h41l75vlb4z45kzgjjmsjxvcv1qk7-mesa-6.4'
    <arg choice='plain'><option>--tree</option></arg>
    <arg choice='plain'><option>--binding</option> <replaceable>name</replaceable></arg>
    <arg choice='plain'><option>--hash</option></arg>
-    <arg choice='plain'><option>--roots</option></arg>
  </group>
  <arg><option>--use-output</option></arg>
  <arg><option>-u</option></arg>
@@ -587,20 +630,12 @@ query is applied to the target of the symlink.</para>
  <varlistentry><term><option>--hash</option></term>
  
    <listitem><para>Prints the SHA-256 hash of the contents of the
-    store paths <replaceable>paths</replaceable>.  Since the hash is
+    store path <replaceable>paths</replaceable>.  Since the hash is
    stored in the Nix database, this is a fast
    operation.</para></listitem>

  </varlistentry>

-  <varlistentry><term><option>--roots</option></term>
-  
-    <listitem><para>Prints the garbage collector roots that point,
-    directly or indirectly, at the store paths
-    <replaceable>paths</replaceable>.</para></listitem>
-
-  </varlistentry>
-
 </variablelist>

 </refsection>
@@ -678,18 +713,6 @@ $ gv graph.ps</screen>

 </para>

-<para>Show every garbage collector root that points to a store path
-that depends on <command>svn</command>:
-
-<screen>
-$ nix-store -q --roots $(which svn)
-/nix/var/nix/profiles/default-81-link
-/nix/var/nix/profiles/default-82-link
-/nix/var/nix/profiles/per-user/eelco/profile-97-link
-</screen>
-
-</para>
-
 </refsection>


--- a/doc/manual/nix-worker.xml
+++ b/doc/manual/nix-worker.xml
@@ -1,7 +1,6 @@
 <refentry xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
-          xmlns:xi="http://www.w3.org/2001/XInclude"
-          xml:id="sec-nix-worker">
+          xmlns:xi="http://www.w3.org/2001/XInclude">

 <refmeta>
  <refentrytitle>nix-worker</refentrytitle>
--- a/doc/manual/package-management.xml
+++ b/doc/manual/package-management.xml
@@ -38,7 +38,7 @@ to end-user applications like Mozilla Firefox.  (Nix is however not
 tied to the Nix Package collection; you could write your own Nix
 expressions based on it, or completely new ones.)  You can download
 the latest version from <link
-xlink:href='http://nixos.org/nixpkgs/download.html' />.</para>
+xlink:href='http://nixos.org/releases/full-index-nixpkgs.html' />.</para>

 <para>Assuming that you have downloaded and unpacked a release of Nix
 Packages, you can view the set of available packages in the release:
@@ -331,7 +331,7 @@ default profile, respectively.  If the profile doesn’t exist, it will
 be created automatically.  You should be careful about storing a
 profile in another location than the <filename>profiles</filename>
 directory, since otherwise it might not be used as a root of the
-garbage collector (see <xref linkend='sec-garbage-collection'
+garbage collector (see section <xref linkend='sec-garbage-collection'
 />).</para>

 <para>All <command>nix-env</command> operations work on the profile
@@ -496,7 +496,7 @@ available in the subscribed channels.</para>

 <para>Often, when you want to install a specific package (e.g., from
 the <link
-xlink:href="http://nixos.org/nixpkgs/">Nix
+xlink:href="http://nixos.org/releases/nixpkgs/nixpkgs-unstable/">Nix
 Packages collection</link>), subscribing to a channel is a bit
 cumbersome.  And channels don’t help you at all if you want to install
 an older version of a package than the one provided by the current
@@ -507,16 +507,19 @@ click on it, and it will be installed with all the necessary
 dependencies.</para>

 <para>For instance, you can go to <link
-xlink:href="http://hydra.nixos.org/jobset/nixpkgs/trunk/channel/latest"
-/> and click on any link for the individual packages for your
-platform.  The first time you do this, your browser will ask what to
-do with <literal>application/nix-package</literal> files.  You should
-open them with <filename>/nix/bin/nix-install-package</filename>.
-This will open a window that asks you to confirm that you want to
-install the package.  When you answer <literal>Y</literal>, the
-package and all its dependencies will be installed.  This is a binary
-deployment mechanism — you get packages pre-compiled for the selected
-platform type.</para>
+xlink:href="http://nixos.org/releases/nixpkgs/nixpkgs-unstable/" /> —
+or to any older release of Nix Packages — and click on any link for
+the individual packages for your platform (say, <link
+xlink:href='http://nix.cs.uu.nl/dist/nix/nixpkgs-0.10pre6622/pkgs/subversion-1.4.0-i686-linux.nixpkg'><literal>subversion-1.4.0</literal>
+for <literal>i686-linux</literal></link>).  The first time you do
+this, your browser will ask what to do with
+<literal>application/nix-package</literal> files.  You should open
+them with <filename>/nix/bin/nix-install-package</filename>.  This
+will open a window that asks you to confirm that you want to install
+the package.  When you answer <literal>Y</literal>, the package and
+all its dependencies will be installed.  This is a binary deployment
+mechanism — you get packages pre-compiled for the selected platform
+type.</para>

 <para>You can also install <literal>application/nix-package</literal>
 files from the command line directly.  See <xref
--- a/doc/manual/quick-start.xml
+++ b/doc/manual/quick-start.xml
@@ -1,6 +1,5 @@
 <chapter xmlns="http://docbook.org/ns/docbook"
-         xmlns:xlink="http://www.w3.org/1999/xlink"
-         xml:id="chap-quick-start">
+         xmlns:xlink="http://www.w3.org/1999/xlink">

 <title>Quick Start</title>

@@ -11,9 +10,9 @@ to the following chapters.</para>

 <orderedlist>

-<listitem><para>Download a source tarball, RPM or Deb from <link
-xlink:href='http://nixos.org/'/>.  Build source distributions using
-the regular sequence:
+<listitem><para>Download a source tarball or RPM from <link
+xlink:href='http://nixos.org/'/>.  Build source
+distributions using the regular sequence:
        
 <screen>
 $ tar xvfj nix-<replaceable>version</replaceable>.tar.bz2
@@ -21,21 +20,13 @@ $ ./configure
 $ make
 $ make install <lineannotation>(as root)</lineannotation></screen>

-This will install the Nix binaries in <filename>/usr/local</filename>
-and keep the Nix store and other state in <filename>/nix</filename>.
-You can change the former by specifying
-<option>--prefix=<replaceable>path</replaceable></option>.  The
-location of the store can be changed using
-<option>--with-store-dir=<replaceable>path</replaceable></option>.
-However, you shouldn't change the store location, if at all possible,
-since that will make it impossible to use pre-built binaries from the
-Nixpkgs channel and other channels.  The location of the state can be
-changed using
-<option>--localstatedir=<replaceable>path</replaceable>.</option></para></listitem>
-
-<listitem><para>You should add
-<filename><replaceable>prefix</replaceable>/etc/profile.d/nix.sh</filename>
-to your <filename>~/.bashrc</filename> (or some other login
+This will install Nix in <filename>/nix</filename>.  You shouldn't
+change the prefix if at all possible since that will make it
+impossible to use pre-built binaries from the Nixpkgs channel and
+other channels.  Alternatively, you could grab an RPM if you're on an
+RPM-based system.  You should also add
+<filename>/nix/etc/profile.d/nix.sh</filename> to your
+<filename>~/.bashrc</filename> (or some other login
 file).</para></listitem>

 <listitem><para>Subscribe to the Nix Packages channel.
@@ -108,7 +99,7 @@ numbers).</para></listitem>

 <listitem><para>You can also install specific packages directly from
 your web browser.  For instance, you can go to <link
-xlink:href="http://hydra.nixos.org/jobset/nixpkgs/trunk/channel/latest" />
+xlink:href="http://nix.cs.uu.nl/dist/nix/nixpkgs-unstable-latest/" />
 and click on any link for the individual packages for your platform.
 Associate <literal>application/nix-package</literal> with the program
 <filename>/nix/bin/nix-install-package</filename>.  A window should
--- a/doc/manual/release-notes.xml
+++ b/doc/manual/release-notes.xml
@@ -8,63 +8,7 @@

 <!--==================================================================-->

-<section xml:id="ssec-relnotes-0.15"><title>Release 0.15 (March 17, 2010)</title>
-
-<para>This is a bug-fix release.  Among other things, it fixes
-building on Mac OS X (Snow Leopard), and improves the contents of
-<filename>/etc/passwd</filename> and <filename>/etc/group</filename>
-in <literal>chroot</literal> builds.</para>
-
-</section>
-
-
-<!--==================================================================-->
-
-<section xml:id="ssec-relnotes-0.14"><title>Release 0.14 (February 4, 2010)</title>
-
-<para>This release has the following improvements:</para>
-
-<itemizedlist>
-
-  <listitem>
-    <para>The garbage collector now starts deleting garbage much
-    faster than before.  It no longer determines liveness of all paths
-    in the store, but does so on demand.</para>
-  </listitem>
-
-  <listitem>
-    <para>Added a new operation, <command>nix-store --query
-    --roots</command>, that shows the garbage collector roots that
-    directly or indirectly point to the given store paths.</para>
-  </listitem>
-
-  <listitem>
-    <para>Removed support for converting Berkeley DB-based Nix
-    databases to the new schema.</para>
-  </listitem>
-
-  <listitem>
-    <para>Removed the <option>--use-atime</option> and
-    <option>--max-atime</option> garbage collector options.  They were
-    not very useful in practice.</para>
-  </listitem>
-
-  <listitem>
-    <para>On Windows, Nix now requires Cygwin 1.7.x.</para>
-  </listitem>
-
-  <listitem>
-    <para>A few bug fixes.</para>
-  </listitem>
-
-</itemizedlist>
-
-</section>
-
-
-<!--==================================================================-->
-
-<section xml:id="ssec-relnotes-0.13"><title>Release 0.13 (November 5,
+<section xml:id="ssec-relnotes-0.13"><title>Release 0.13 (April NN,
 2009)</title>

 <para>This is primarily a bug fix release.  It has some new
@@ -141,25 +85,7 @@ features:</para>
    add a string to stack traces — useful for debugging),
    <varname>builtins.isBool</varname>,
    <varname>builtins.isString</varname>,
-    <varname>builtins.isInt</varname>,
-    <varname>builtins.intersectAttrs</varname>.</para>
-  </listitem>
-
-  <listitem>
-    <para>OpenSolaris support (Sander van der Burg).</para>
-  </listitem>
-
-  <listitem>
-    <para>Stack traces are no longer displayed unless the
-    <option>--show-trace</option> option is used.</para>
-  </listitem>
-
-  <listitem>
-    <para>The scoping rules for <literal>inherit
-    (<replaceable>e</replaceable>) ...</literal> in recursive
-    attribute sets have changed.  The expression
-    <replaceable>e</replaceable> can now refer to the attributes
-    defined in the containing set.</para>
+    <varname>builtins.isInt</varname>.</para>
  </listitem>

 </itemizedlist>
--- a/doc/manual/writing-nix-expressions.xml
+++ b/doc/manual/writing-nix-expressions.xml
@@ -1106,7 +1106,7 @@ used in the Nix expression for Subversion.</para>
    incompatibility might occur.</para>
  </callout>

-  <callout arearefs='ex-subversion-nix-co-3'>
+  <callout arearefs='ex-subversion-nix-co-2'>
    <para>This assertion says that in order for Subversion to have SSL
    support (so that it can access <literal>https</literal> URLs), an
    OpenSSL library must be passed.  Additionally, it says that
--- a/externals/Makefile.am
+++ b/externals/Makefile.am
@@ -1,3 +1,78 @@
+# Berkeley DB
+
+DB = db-4.5.20
+
+if OLD_DB_COMPAT
+
+$(DB).tar.gz:
+	@echo "Nix requires Berkeley DB to build."
+	@echo "Please download version 4.5.20 from"
+	@echo "  http://download-east.oracle.com/berkeley-db/db-4.5.20.tar.gz"
+	@echo "and place it in the externals/ directory."
+	false
+
+$(DB): $(DB).tar.gz
+	gunzip < $(srcdir)/$(DB).tar.gz | tar xvf -
+	(cd $(DB) && $(patch) -p1) < $(srcdir)/bdb-cygwin.patch
+
+have-db:
+	$(MAKE) $(DB)
+	touch have-db
+
+if HAVE_BDB
+build-db:
+else
+build-db: have-db
+	(pfx=`pwd` && \
+	cd $(DB)/build_unix && \
+	CC="$(CC)" CXX="$(CXX)" CFLAGS="$(CFLAGS)" CXXFLAGS="$(CXXFLAGS)" \
+	 ../dist/configure --prefix=$$pfx/inst-bdb \
+	 --enable-cxx --disable-shared --disable-cryptography \
+         --disable-replication --disable-verify && \
+	$(MAKE) && \
+	$(MAKE) install_include install_lib)
+	touch build-db
+endif
+
+else
+
+build-db:
+
+endif
+
+
+# CWI ATerm
+
+ATERM = aterm-2.4.2-fixes-r2
+
+$(ATERM).tar.bz2:
+	@echo "Nix requires the CWI ATerm library to build."
+	@echo "Please download version 2.4.2-fixes-r2 from"
+	@echo "  http://nixos.org/tarballs/aterm-2.4.2-fixes-r2.tar.bz2"
+	@echo "and place it in the externals/ directory."
+	false
+
+$(ATERM): $(ATERM).tar.bz2
+	bunzip2 < $(srcdir)/$(ATERM).tar.bz2 | tar xvf -
+
+have-aterm:
+	$(MAKE) $(ATERM)
+	touch have-aterm
+
+if HAVE_ATERM
+build-aterm:
+else
+build-aterm: have-aterm
+	(pfx=`pwd` && \
+	cd $(ATERM) && \
+	CC="$(CC)" ./configure --prefix=$$pfx/inst-aterm \
+	  --disable-shared --enable-static && \
+	$(MAKE) && \
+	$(MAKE) install)
+	touch build-aterm
+endif
+
+
 # bzip2

 BZIP2 = bzip2-1.0.5
@@ -32,10 +107,11 @@ install:
 endif


-all: build-bzip2
+all: build-db build-aterm build-bzip2

-EXTRA_DIST = $(BZIP2).tar.gz
+EXTRA_DIST = $(DB).tar.gz $(ATERM).tar.bz2 $(BZIP2).tar.gz \
+  bdb-cygwin.patch

 ext-clean:
-	$(RM) -f have-bzip2 build-bzip2
-	$(RM) -rf $(BZIP2)
+	$(RM) -f have-db build-db have-aterm build-aterm have-bzip2 build-bzip2
+	$(RM) -rf $(DB) $(ATERM) $(BZIP2)
--- a/externals/bdb-cygwin.patch
+++ b/externals/bdb-cygwin.patch
@@ -0,0 +1,22 @@
+diff -rc db-4.5.20-orig/os/os_flock.c db-4.5.20/os/os_flock.c
+*** db-4.5.20-orig/os/os_flock.c	2006-10-13 12:36:12.000000000 +0200
+--- db-4.5.20/os/os_flock.c	2006-10-13 12:40:11.000000000 +0200
+***************
+*** 30,35 ****
+--- 30,44 ----
+  
+  	DB_ASSERT(dbenv, F_ISSET(fhp, DB_FH_OPENED) && fhp->fd != -1);
+  
+ #ifdef __CYGWIN__
+ 	/*
+ 	 * Windows file locking interferes with read/write operations, so we
+ 	 * map the ranges to an area past the end of the file.
+ 	 */
+ 	DB_ASSERT(dbenv, offset < (off_t) 1 << 62);
+ 	offset += (off_t) 1 << 62;
+ #endif
+ 
+  	fl.l_start = offset;
+  	fl.l_len = 1;
+  	fl.l_type = acquire ? F_WRLCK : F_UNLCK;
+Only in db-4.5.20/os: os_flock.c~
--- a/release.nix
+++ b/release.nix
@@ -18,10 +18,7 @@ let
        src = nix;
        inherit officialRelease;

-        buildInputs =
-          [ curl bison flex2533 perl libxml2 libxslt w3m bzip2
-            tetex dblatex nukeReferences
-          ];
+        buildInputs = [curl bison flex2533 perl libxml2 libxslt w3m bzip2 jing_tools tetex dblatex];

        configureFlags = ''
          --with-docbook-rng=${docbook5}/xml/rng/docbook
@@ -29,13 +26,27 @@ let
          --with-xml-flags=--nonet
        '';

-        # Include the Bzip2 tarball in the distribution.
+        # Include the BDB, ATerm and Bzip2 tarballs in the distribution.
        preConfigure = ''
+          stripHash ${db45.src}
+          # Remove unnecessary stuff from the Berkeley DB tarball.
+          ( mkdir bdb-temp
+            cd bdb-temp
+            tar xfz ${db45.src}
+            cd *
+            rm -rf docs test tcl perl libdb_java java rpc_server build_vxworks \
+              examples_java examples_c examples_cxx dist/tags
+            mkdir test
+            touch test/include.tcl
+            cd ..
+            tar cvfz ../externals/$strippedName *
+          )
+
+          stripHash ${aterm242fixes.src}
+          cp -pv ${aterm242fixes.src} externals/$strippedName
+
          stripHash ${bzip2.src}
          cp -pv ${bzip2.src} externals/$strippedName
-
-          # TeX needs a writable font cache.
-          export VARTEXFONTS=$TMPDIR/texfonts
        '';

        preDist = ''
@@ -43,14 +54,6 @@ let
          
          make -C doc/manual manual.pdf prefix=$out
          cp doc/manual/manual.pdf $out/manual.pdf
-
-          # The PDF containes filenames of included graphics (see
-          # http://www.tug.org/pipermail/pdftex/2007-August/007290.html).
-          # This causes a retained dependency on dblatex, which Hydra
-          # doesn't like (the output of the tarball job is distributed
-          # to Windows and Macs, so there should be no Linux binaries
-          # in the closure).
-          nuke-refs $out/manual.pdf
          
          echo "doc manual $out/share/doc/nix/manual" >> $out/nix-support/hydra-build-products
          echo "doc-pdf manual $out/manual.pdf" >> $out/nix-support/hydra-build-products
@@ -74,12 +77,11 @@ let

        configureFlags = ''
          --disable-init-state
-          --with-bzip2=${bzip2}
+          --with-bdb=${db45} --with-aterm=${aterm242fixes} --with-bzip2=${bzip2}
        '';
      };

-
-    /*
+      
    static =
      { tarball ? jobs.tarball {}
      , system ? "i686-linux"
@@ -95,11 +97,10 @@ let

        configureFlags = ''
          --disable-init-state
-          --with-bzip2=${bzip2}
+          --disable-old-db-compat --with-aterm=${aterm242fixes} --with-bzip2=${bzip2}
          --enable-static-nix
        '';
      };
-    */

      
    coverage =
@@ -120,7 +121,7 @@ let

        configureFlags = ''
          --disable-init-state --disable-shared
-          --with-bzip2=${bzip2}
+          --with-bdb=${db45} --with-aterm=${aterm242fixes} --with-bzip2=${bzip2}
        '';

        lcovFilter = ["*/boost/*" "*-tab.*"];
@@ -132,32 +133,22 @@ let
      };

      
-    rpm_fedora5i386 = makeRPM_i686 (diskImages: diskImages.fedora5i386) 10;
-    rpm_fedora9i386 = makeRPM_i686 (diskImages: diskImages.fedora9i386) 20;
-    rpm_fedora9x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora9x86_64) 20;
-    rpm_fedora10i386 = makeRPM_i686 (diskImages: diskImages.fedora10i386) 30;
-    rpm_fedora10x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora10x86_64) 30;
-    rpm_fedora11i386 = makeRPM_i686 (diskImages: diskImages.fedora11i386) 40;
-    rpm_fedora11x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora11x86_64) 40;
-    rpm_fedora12i386 = makeRPM_i686 (diskImages: diskImages.fedora12i386) 50;
-    rpm_fedora12x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora12x86_64) 50;
+    rpm_fedora5i386 = makeRPM_i686 (diskImages: diskImages.fedora5i386) 20;
+    rpm_fedora9i386 = makeRPM_i686 (diskImages: diskImages.fedora9i386) 50;
+    rpm_fedora9x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora9x86_64) 50;
+    rpm_fedora10i386 = makeRPM_i686 (diskImages: diskImages.fedora10i386) 40;
+    rpm_fedora10x86_64 = makeRPM_x86_64 (diskImages: diskImages.fedora10x86_64) 40;
    rpm_opensuse103i386 = makeRPM_i686 (diskImages: diskImages.opensuse103i386) 40;
-    rpm_opensuse110i386 = makeRPM_i686 (diskImages: diskImages.opensuse110i386) 50;
-    rpm_opensuse110x86_64 = makeRPM_x86_64 (diskImages: diskImages.opensuse110x86_64) 50;

    
    deb_debian40i386 = makeDeb_i686 (diskImages: diskImages.debian40i386) 40;
    deb_debian40x86_64 = makeDeb_x86_64 (diskImages: diskImages.debian40x86_64) 40;
-    deb_debian50i386 = makeDeb_i686 (diskImages: diskImages.debian50i386) 50;
-    deb_debian50x86_64 = makeDeb_x86_64 (diskImages: diskImages.debian50x86_64) 50;
-    deb_ubuntu804i386 = makeDeb_i686 (diskImages: diskImages.ubuntu804i386) 20;
-    deb_ubuntu804x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu804x86_64) 20;
-    deb_ubuntu810i386 = makeDeb_i686 (diskImages: diskImages.ubuntu810i386) 30;
-    deb_ubuntu810x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu810x86_64) 30;
-    deb_ubuntu904i386 = makeDeb_i686 (diskImages: diskImages.ubuntu904i386) 40;
-    deb_ubuntu904x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu904x86_64) 40;
-    deb_ubuntu910i386 = makeDeb_i686 (diskImages: diskImages.ubuntu910i386) 50;
-    deb_ubuntu910x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu910x86_64) 50;
+    deb_debian50i386 = makeDeb_i686 (diskImages: diskImages.debian50i386) 30;
+    deb_debian50x86_64 = makeDeb_x86_64 (diskImages: diskImages.debian50x86_64) 30;
+    deb_ubuntu804i386 = makeDeb_i686 (diskImages: diskImages.ubuntu804i386) 50;
+    deb_ubuntu804x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu804x86_64) 50;
+    deb_ubuntu810i386 = makeDeb_i686 (diskImages: diskImages.ubuntu810i386) 40;
+    deb_ubuntu810x86_64 = makeDeb_x86_64 (diskImages: diskImages.ubuntu810x86_64) 40;


  };
@@ -199,7 +190,6 @@ let
      memSize = 1024;
      meta = { schedulingPriority = toString prio; };
      configureFlags = "--sysconfdir=/etc";
-      debRequires = ["curl"];
    };


--- a/scripts/Makefile.am
+++ b/scripts/Makefile.am
@@ -15,7 +15,6 @@ install-exec-local: readmanifest.pm download-using-manifests.pl copy-from-other-
 	$(INSTALL) -d $(DESTDIR)$(libexecdir)/nix
 	$(INSTALL_DATA) readmanifest.pm $(DESTDIR)$(libexecdir)/nix 
 	$(INSTALL_DATA) readconfig.pm $(DESTDIR)$(libexecdir)/nix 
-	$(INSTALL_DATA) ssh.pm $(DESTDIR)$(libexecdir)/nix 
 	$(INSTALL_PROGRAM) find-runtime-roots.pl $(DESTDIR)$(libexecdir)/nix 
 	$(INSTALL_PROGRAM) generate-patches.pl $(DESTDIR)$(libexecdir)/nix 
 	$(INSTALL_PROGRAM) build-remote.pl $(DESTDIR)$(libexecdir)/nix 
@@ -32,7 +31,6 @@ EXTRA_DIST = nix-collect-garbage.in \
  nix-channel.in \
  readmanifest.pm.in \
  readconfig.pm.in \
-  ssh.pm \
  nix-build.in \
  download-using-manifests.pl.in \
  copy-from-other-stores.pl.in \
--- a/scripts/build-remote.pl.in
+++ b/scripts/build-remote.pl.in
@@ -1,10 +1,9 @@
-#! @perl@ -w -I@libexecdir@/nix
+#! @perl@ -w

+use strict;
 use Fcntl ':flock';
 use English '-no_match_vars';
 use IO::Handle;
-use ssh qw/sshOpts openSSHConnection/;
-

 # General operation:
 #
@@ -23,14 +22,6 @@ use ssh qw/sshOpts openSSHConnection/;
 # The nice thing about this scheme is that if we die prematurely, the
 # locks are released automatically.

-
-# Make sure that we don't get any SSH passphrase or host key popups -
-# if there is any problem it should fail, not do something
-# interactive.
-$ENV{"DISPLAY"} = "";
-$ENV{"SSH_ASKPASS"} = "";
-
-
 my $loadIncreased = 0;

 my ($amWilling, $localSystem, $neededSystem, $drvPath, $maxSilentTime) = @ARGV;
@@ -56,22 +47,24 @@ decline if !defined $conf || ! -e $conf;
 my $canBuildLocally = $amWilling && ($localSystem eq $neededSystem);


-# Read the list of machines.
+# Otherwise find a willing remote machine.
 my @machines;
+my %curJobs;
+
+
+# Read the list of machines.
 open CONF, "< $conf" or die;

 while (<CONF>) {
    chomp;
    s/\#.*$//g;
    next if /^\s*$/;
-    /^\s*(\S+)\s+(\S+)\s+(\S+)\s+(\d+)(\s+([0-9\.]+))?\s*$/ or die;
+    /^\s*(\S+)\s+(\S+)\s+(\S+)\s+(\d+)\s*$/ or die;
    push @machines,
        { hostName => $1
-        , systemTypes => [split(/,/, $2)]
+        , systemType => $2
        , sshKeys => $3
        , maxJobs => $4
-        , speedFactor => 1.0 * ($6 || 1)
-        , enabled => 1
        };
 }

@@ -84,105 +77,50 @@ open MAINLOCK, ">>$mainLock" or die;
 flock(MAINLOCK, LOCK_EX) or die;


-sub openSlotLock {
-    my ($machine, $slot) = @_;
-    my $slotLockFn = "$currentLoad/" . (join '+', @{$machine->{systemTypes}}) . "-" . $machine->{hostName} . "-$slot";
-    my $slotLock = new IO::Handle;
-    open $slotLock, ">>$slotLockFn" or die;
-    return $slotLock;
-}
-    
-
-my $hostName;
+# Find a suitable system.
+my $rightType = 0;
+my $machine;
 my $slotLock;
+LOOP: foreach my $cur (@machines) {
+    if ($neededSystem eq $cur->{systemType}
+        || ($neededSystem eq "i686-linux" && $cur->{systemType} eq "x86_64-linux"))
+    {
+        $rightType = 1;

-while (1) {
-    
-    # Find all machine that can execute this build, i.e., that support
-    # builds for the given platform and are not at their job limit.
-    my $rightType = 0;
-    my @available = ();
-    LOOP: foreach my $cur (@machines) {
-        if ($cur->{enabled} && grep { $neededSystem eq $_ } @{$cur->{systemTypes}}) {
-            $rightType = 1;
-
-            # We have a machine of the right type.  Determine the load on
-            # the machine.
-            my $slot = 0;
-            my $load = 0;
-            my $free;
-            while ($slot < $cur->{maxJobs}) {
-                my $slotLock = openSlotLock($cur, $slot);
-                if (flock($slotLock, LOCK_EX | LOCK_NB)) {
-                    $free = $slot unless defined $free;
-                    flock($slotLock, LOCK_UN) or die;
-                } else {
-                    $load++;
-                }
-                close $slotLock;
-                $slot++;
+        # We have a machine of the right type.  Try to get a lock on
+        # one of the machine's lock files.
+        my $slot = 0;
+        while ($slot < $cur->{maxJobs}) {
+            my $slotLockFn = "$currentLoad/" . $cur->{systemType} . "-" . $cur->{hostName} . "-$slot";
+            $slotLock = new IO::Handle;
+            open $slotLock, ">>$slotLockFn" or die;
+            if (flock($slotLock, LOCK_EX | LOCK_NB)) {
+                utime undef, undef, $slotLock;
+                $machine = $cur;
+                last LOOP;
            }
-
-            push @available, { machine => $cur, load => $load, free => $free }
-            if $load < $cur->{maxJobs};
+            close $slotLock;
+            $slot++;
        }
    }
-
-    if (defined $ENV{NIX_DEBUG_HOOK}) {
-        print STDERR "load on " . $_->{machine}->{hostName} . " = " . $_->{load} . "\n"
-            foreach @available;
-    }
-
-
-    # Didn't find any available machine?  Then decline or postpone.
-    if (scalar @available == 0) {
-        # Postpone if we have a machine of the right type, except if the
-        # local system can and wants to do the build.
-        if ($rightType && !$canBuildLocally) {
-            sendReply "postpone";
-            exit 0;
-        } else {
-            decline;
-        }
-    }
-
-
-    # Prioritise the available machines as follows:
-    # - First by load divided by speed factor, rounded to the nearest
-    #   integer.  This causes fast machines to be preferred over slow
-    #   machines with similar loads.
-    # - Then by speed factor.
-    # - Finally by load.
-    sub lf { my $x = shift; return int($x->{load} / $x->{machine}->{speedFactor} + 0.4999); }
-    @available = sort
-        { lf($a) <=> lf($b)
-              || $b->{machine}->{speedFactor} <=> $a->{machine}->{speedFactor}
-              || $a->{load} <=> $b->{load}
-        } @available;
-
-
-    # Select the best available machine and lock a free slot.
-    my $selected = $available[0]; 
-    my $machine = $selected->{machine};
-
-    $slotLock = openSlotLock($machine, $selected->{free});
-    flock($slotLock, LOCK_EX | LOCK_NB) or die;
-    utime undef, undef, $slotLock;
-
-    close MAINLOCK;
-
-
-    # Connect to the selected machine.
-    @sshOpts = ("-i", $machine->{sshKeys}, "-x");
-    $hostName = $machine->{hostName};
-    last if openSSHConnection $hostName;
-    
-    warn "unable to open SSH connection to $hostName, trying other available machines...\n";
-    $machine->{enabled} = 0;
 }

+close MAINLOCK;

-# Tell Nix we've accepted the build.
+
+# Didn't find one?  Then decline or postpone.
+if (!defined $machine) {
+    # Postpone if we have a machine of the right type, except if the
+    # local system can and wants to do the build.
+    if ($rightType && !$canBuildLocally) {
+        sendReply "postpone";
+        exit 0;
+    } else {
+        decline;
+    }
+}
+
+# Yes we did, accept.
 sendReply "accept";
 my $x = <STDIN>;
 chomp $x;
@@ -192,9 +130,43 @@ if ($x ne "okay") {
 }


-# Do the actual build.
+# Do the actual job.
+my $hostName = $machine->{hostName};
 print STDERR "building `$drvPath' on `$hostName'\n";

+# Make sure that we don't get any SSH passphrase or host key popups -
+# if there is any problem it should fail, not do something
+# interactive.
+$ENV{"DISPLAY"} = "";
+$ENV{"SSH_PASSWORD_FILE="} = "";
+$ENV{"SSH_ASKPASS="} = "";
+
+my $sshOpts = "-i " . $machine->{sshKeys} . " -x";
+
+# Hack to support Cygwin: if we login without a password, we don't
+# have exactly the same rights as when we do.  This causes the
+# Microsoft C compiler to fail with certain flags:
+#
+#   http://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=99676
+#
+# So as a workaround, we pass a verbatim password.  ssh tries to makes
+# this very hard; the trick is to make it call SSH_ASKPASS to get the
+# password.  (It only calls this command when there is no controlling
+# terminal, but Nix ensures that is is the case.  When doing this
+# manually, use setsid(1).)
+if ($machine->{sshKeys} =~ /^password:/) {
+    my $passwordFile = $machine->{sshKeys};
+    $passwordFile =~ s/^password://;
+    $sshOpts = "ssh -x";
+    $ENV{"SSH_PASSWORD_FILE"} = $passwordFile;
+    $ENV{"SSH_ASKPASS"} = "/tmp/writepass";
+
+    open WRITEPASS, ">/tmp/writepass" or die;
+    print WRITEPASS "#! /bin/sh\ncat \"\$SSH_PASSWORD_FILE\"";
+    close WRITEPASS;
+    chmod 0755, "/tmp/writepass" or die;
+}
+
 my $inputs = `cat inputs`; die if ($? != 0);
 $inputs =~ s/\n/ /g;

@@ -206,7 +178,7 @@ print "copying inputs...\n";
 my $maybeSign = "";
 $maybeSign = "--sign" if -e "/nix/etc/nix/signing-key.sec";

-system("NIX_SSHOPTS=\"@sshOpts\" @bindir@/nix-copy-closure $hostName $maybeSign $drvPath $inputs") == 0
+system("NIX_SSHOPTS=\"$sshOpts\" @bindir@/nix-copy-closure --gzip $hostName $maybeSign $drvPath $inputs") == 0
    or die "cannot copy inputs to $hostName: $?";

 print "building...\n";
@@ -218,10 +190,10 @@ my $buildFlags = "--max-silent-time $maxSilentTime";
 # connection dies.  Without it, the remote process might continue to
 # run indefinitely (that is, until it next tries to write to
 # stdout/stderr).
-if (system("ssh $hostName @sshOpts -tt 'nix-store --realise $buildFlags $drvPath > /dev/null'") != 0) {
+if (system("ssh -tt $sshOpts $hostName 'nix-store --realise -K $buildFlags $drvPath > /dev/null'") != 0) {
    # If we couldn't run ssh or there was an ssh problem (indicated by
    # exit code 255), then we return exit code 1; otherwise we assume
-    # that the builder failed, which we indicate to Nix using exit
+    # that the builder failed, which we indicated to Nix using exit
    # code 100.  It's important to distinguish between the two because
    # the first is a transient failure and the latter is permanent.
    my $res = $? == -1 || ($? >> 8) == 255 ? 1 : 100;
@@ -235,6 +207,6 @@ foreach my $output (split '\n', $outputs) {
    my $maybeSignRemote = "";
    $maybeSignRemote = "--sign" if $UID != 0;
    
-    system("ssh $hostName @sshOpts 'nix-store --export $maybeSignRemote $output' | @bindir@/nix-store --import > /dev/null") == 0
+    system("ssh $sshOpts $hostName 'nix-store --export $maybeSignRemote $output | gzip' | gunzip | @bindir@/nix-store --import > /dev/null") == 0
 	or die "cannot copy $output from $hostName: $?";
 }
--- a/scripts/download-using-manifests.pl.in
+++ b/scripts/download-using-manifests.pl.in
@@ -73,7 +73,7 @@ if ($ARGV[0] eq "--query") {
 }

 elsif ($ARGV[0] ne "--substitute") {
-    die;
+    die "syntax: $0 [--query-paths | --query-info PATHS... | --substitute PATH]\n";
 }


@@ -85,6 +85,8 @@ my $targetPath = $ARGV[1];
 my $tmpDir = tempdir("nix-download.XXXXXX", CLEANUP => 1, TMPDIR => 1)
    or die "cannot create a temporary directory";

+chdir $tmpDir or die "cannot change to `$tmpDir': $!";
+
 my $tmpNar = "$tmpDir/nar";
 my $tmpNar2 = "$tmpDir/nar2";

--- a/scripts/nix-build.in
+++ b/scripts/nix-build.in
@@ -12,7 +12,6 @@ my $outLink;
 my $drvLink;

 my $dryRun = 0;
-my $verbose = 0;

 my @instArgs = ();
 my @buildArgs = ();
@@ -113,16 +112,6 @@ EOF
        $dryRun = 1;
    }
    
-    elsif ($arg eq "--show-trace") {
-        push @instArgs, $arg;
-    }
-    
-    elsif ($arg eq "--verbose" or substr($arg, 0, 2) eq "-v") {
-        push @buildArgs, $arg;
-        push @instArgs, $arg;
-        $verbose = 1;
-    }
-    
    elsif (substr($arg, 0, 1) eq "-") {
        push @buildArgs, $arg;
    }
@@ -160,7 +149,7 @@ foreach my $expr (@exprs) {

    foreach my $drvPath (@drvPaths) {
        my $target = readlink $drvPath or die "cannot read symlink `$drvPath'";
-        print STDERR "derivation is $target\n" if $verbose;
+        print STDERR "store derivation is $target\n";
    }

    # Build.
--- a/scripts/nix-channel.in
+++ b/scripts/nix-channel.in
@@ -78,9 +78,6 @@ sub removeChannel {
 sub update {
    readChannels;

-    # Create the manifests directory if it doesn't exist.
-    mkdir "$stateDir/manifests", 0755 unless -e "$stateDir/manifests";
-
    # Do we have write permission to the manifests directory?  If not,
    # then just skip pulling the manifest and just download the Nix
    # expressions.  If the user is a non-privileged user in a
@@ -88,6 +85,11 @@ sub update {
    # source.
    if (-W "$stateDir/manifests") {

+        # Remove all the old manifests.
+        for my $manifest (glob "$stateDir/manifests/*.nixmanifest") {
+            unlink $manifest or die "cannot remove `$manifest': $!";
+        }
+
        # Pull cache manifests.
        foreach my $url (@channels) {
            #print "pulling cache manifest from `$url'\n";
--- a/scripts/nix-copy-closure.in
+++ b/scripts/nix-copy-closure.in
@@ -1,6 +1,4 @@
-#! @perl@ -w -I@libexecdir@/nix
-
-use ssh;
+#! @perl@ -w

 my $binDir = $ENV{"NIX_BIN_DIR"} || "@bindir@";

@@ -16,11 +14,12 @@ EOF

 # Get the target host.
 my $sshHost;
+my @sshOpts = split ' ', ($ENV{"NIX_SSHOPTS"} or "");

 my $sign = 0;

-my $compressor = "";
-my $decompressor = "";
+my $compressor = "cat";
+my $decompressor = "cat";

 my $toMode = 1;

@@ -35,8 +34,8 @@ while (@ARGV) {
        $sign = 1;
    }
    elsif ($arg eq "--gzip") {
-        $compressor = "| gzip";
-        $decompressor = "gunzip |";
+        $compressor = "gzip";
+        $decompressor = "gunzip";
    }
    elsif ($arg eq "--from") {
        $toMode = 0;
@@ -53,9 +52,6 @@ while (@ARGV) {
 }


-openSSHConnection $sshHost or die "$0: unable to start SSH\n";
-
-
 if ($toMode) { # Copy TO the remote machine.

    my @allStorePaths;
@@ -73,10 +69,11 @@ if ($toMode) { # Copy TO the remote machine.


    # Ask the remote host which paths are invalid.
-    open(READ, "ssh $sshHost @sshOpts nix-store --check-validity --print-invalid @allStorePaths|");
+    open(READ, "ssh @sshOpts $sshHost nix-store --check-validity --print-invalid @allStorePaths|");
    my @missing = ();
    while (<READ>) {
        chomp;
+        print STDERR "target machine needs $_\n";
        push @missing, $_;
    }
    close READ or die;
@@ -84,11 +81,9 @@ if ($toMode) { # Copy TO the remote machine.

    # Export the store paths and import them on the remote machine.
    if (scalar @missing > 0) {
-        print STDERR "copying these missing paths:\n";
-        print STDERR "  $_\n" foreach @missing;
        my $extraOpts = "";
        $extraOpts .= "--sign" if $sign == 1;
-        system("nix-store --export $extraOpts @missing $compressor | ssh $sshHost @sshOpts '$decompressor nix-store --import'") == 0
+        system("nix-store --export $extraOpts @missing | $compressor | ssh @sshOpts $sshHost '$decompressor | nix-store --import'") == 0
            or die "copying store paths to remote machine `$sshHost' failed: $?";
    }

@@ -119,6 +114,7 @@ else { # Copy FROM the remote machine.
    my @missing = ();
    while (<READ>) {
        chomp;
+        print STDERR "local machine needs $_\n";
        push @missing, $_;
    }
    close READ or die;
@@ -126,12 +122,10 @@ else { # Copy FROM the remote machine.

    # Export the store paths on the remote machine and import them on locally.
    if (scalar @missing > 0) {
-        print STDERR "copying these missing paths:\n";
-        print STDERR "  $_\n" foreach @missing;
        my $extraOpts = "";
        $extraOpts .= "--sign" if $sign == 1;
-        system("ssh $sshHost @sshOpts 'nix-store --export $extraOpts @missing $compressor' | $decompressor @bindir@/nix-store --import") == 0
-            or die "copying store paths from remote machine `$sshHost' failed: $?";
+        system("ssh @sshOpts $sshHost 'nix-store --export $extraOpts @missing | $compressor' | $decompressor | @bindir@/nix-store --import") == 0
+            or die "copying store paths to remote machine `$sshHost' failed: $?";
    }

 }
--- a/scripts/nix-prefetch-url.in
+++ b/scripts/nix-prefetch-url.in
@@ -21,10 +21,7 @@ if test -z "$url"; then
    exit 1
 fi

-# Handle escaped characters in the URI.  `+', `=' and `?' are the only
-# characters that are valid in Nix store path names but have a special
-# meaning in URIs.
-name=$(basename "$url" | @sed@ -e 's/%2b/+/g' -e 's/%3d/=/g' -e 's/%3f/\?/g')
+name=$(basename "$url")
 if test -z "$name"; then echo "invalid url"; exit 1; fi


--- a/scripts/nix-pull.in
+++ b/scripts/nix-pull.in
@@ -18,12 +18,6 @@ my $manifestDir = ($ENV{"NIX_MANIFESTS_DIR"} or "$stateDir/manifests");
 umask 0022;


-# Create the manifests directory if it doesn't exist.
-if (! -e $manifestDir) {
-    mkdir $manifestDir, 0755 or die "cannot create directory `$manifestDir'";
-}
-
-
 # Process the URLs specified on the command line.
 my %narFiles;
 my %localPaths;
@@ -51,7 +45,7 @@ sub processURL {

    # First see if a bzipped manifest is available.
    if (system("@curl@ --fail --silent --head '$url'.bz2 > /dev/null") == 0) {
-        print "fetching list of Nix archives at `$url.bz2'...\n";
+        print "obtaining list of Nix archives at `$url.bz2'...\n";
        my $bzipped = downloadFile "$url.bz2";

        $manifest = "$tmpDir/MANIFEST";
@@ -92,31 +86,11 @@ sub processURL {
    my $hash = `$binDir/nix-hash --flat '$manifest'`
        or die "cannot hash `$manifest'";
    chomp $hash;
-
-    my $urlFile = "$manifestDir/$baseName-$hash.url";
-    open URL, ">$urlFile" or die "cannot create `$urlFile'";
-    print URL "$url";
-    close URL;
    
    my $finalPath = "$manifestDir/$baseName-$hash.nixmanifest";
-
-    unlink $finalPath if -e $finalPath;
-        
-    symlink("$manifest", "$finalPath")
+    
+    system("@coreutils@/ln", "-sfn", "$manifest", "$finalPath") == 0
        or die "cannot link `$finalPath to `$manifest'";
-
-    # Delete all old manifests downloaded from this URL.
-    for my $urlFile2 (glob "$manifestDir/*.url") {
-        next if $urlFile eq $urlFile2;
-        open URL, "<$urlFile2" or die;
-        my $url2 = <URL>;
-        chomp $url2;
-        close URL;
-        next unless $url eq $url2;
-        my $base = $urlFile2; $base =~ s/.url$//;
-        unlink "${base}.url";
-        unlink "${base}.nixmanifest";
-    }
 }

 while (@ARGV) {
--- a/scripts/ssh.pm
+++ b/scripts/ssh.pm
@@ -1,47 +0,0 @@
-use strict;
-use File::Temp qw(tempdir);
-
-our @sshOpts = split ' ', ($ENV{"NIX_SSHOPTS"} or "");
-
-my $sshStarted = 0;
-my $sshHost;
-
-# Open a master SSH connection to `host', unless there already is a
-# running master connection (as determined by `-O check').
-sub openSSHConnection {
-    my ($host) = @_;
-    die if $sshStarted;
-    $sshHost = $host;
-    return 1 if system("ssh $sshHost @sshOpts -O check 2> /dev/null") == 0;
-
-    my $tmpDir = tempdir("nix-ssh.XXXXXX", CLEANUP => 1, TMPDIR => 1)
-        or die "cannot create a temporary directory";
-    
-    push @sshOpts, "-S", "$tmpDir/control";
-
-    # Start the master.  We can't use the `-f' flag (fork into
-    # background after establishing the connection) because then the
-    # child continues to run if we are killed.  So instead make SSH
-    # print "started" when it has established the connection, and wait
-    # until we see that.
-    open SSH, "ssh $sshHost @sshOpts -M -N -o LocalCommand='echo started' -o PermitLocalCommand=yes |" or die;
-    while (<SSH>) {
-        chomp;
-        last if /started/;
-    }
-    
-    $sshStarted = 1;
-    return 1;
-}
-
-# Tell the master SSH client to exit.
-sub closeSSHConnection {
-    if ($sshStarted) {
-        system("ssh $sshHost @sshOpts -O exit 2> /dev/null") == 0
-            or warn "unable to stop SSH master: $?";
-    }
-}
-
-END { my $saved = $?; closeSSHConnection; $? = $saved; }
-
-return 1;
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1,3 +1,5 @@
 SUBDIRS = bin2c boost libutil libstore libmain nix-store nix-hash \
 libexpr nix-instantiate nix-env nix-worker nix-setuid-helper \
 nix-log2xml bsdiff-4.3
+
+EXTRA_DIST = aterm-helper.pl
--- a/src/aterm-helper.pl
+++ b/src/aterm-helper.pl
@@ -0,0 +1,178 @@
+#! /usr/bin/perl -w
+
+# This program generates C/C++ code for efficiently manipulating
+# ATerms.  It generates functions to build and match ATerms according
+# to a set of constructor definitions defined in a file read from
+# standard input.  A constructor is defined by a line with the
+# following format:
+#
+#   SYM | ARGS | TYPE | FUN?
+#
+# where SYM is the name of the constructor, ARGS is a
+# whitespace-separated list of argument types, TYPE is the type of the
+# resulting ATerm (which should be `ATerm' or a type synonym for
+# `ATerm'), and the optional FUN is used to construct the names of the
+# build and match functions (it defaults to SYM; overriding it is
+# useful if there are overloaded constructors, e.g., with different
+# arities).  Note that SYM may be empty.
+#
+# A line of the form
+#
+#   VAR = EXPR
+#
+# causes a ATerm variable to be generated that is initialised to the
+# value EXPR.
+#
+# Finally, a line of the form
+#
+#   init NAME
+#
+# causes the initialisation function to be called `NAME'.  This
+# function must be called before any of the build/match functions or
+# the generated variables are used.
+
+die if scalar @ARGV != 2;
+
+my $syms = "";
+my $init = "";
+my $initFun = "init";
+
+open HEADER, ">$ARGV[0]";
+open IMPL, ">$ARGV[1]";
+
+print HEADER "#include <aterm2.h>\n";
+print HEADER "#ifdef __cplusplus\n";
+print HEADER "namespace nix {\n";
+print HEADER "#endif\n\n\n";
+print IMPL "namespace nix {\n";
+
+while (<STDIN>) {
+    s/\#.*//;
+    next if (/^\s*$/);
+    
+    if (/^\s*(\w*)\s*\|([^\|]*)\|\s*(\w+)\s*\|\s*(\w+)?/) {
+        my $const = $1;
+        my @types = split ' ', $2;
+        my $result = $3;
+        my $funname = $4;
+        $funname = $const unless defined $funname;
+
+        my $formals = "";
+        my $formals2 = "";
+        my $args = "";
+        my $unpack = "";
+        my $n = 1;
+        foreach my $type (@types) {
+            my $realType = $type;
+            $args .= ", ";
+            if ($type eq "string") {
+#                $args .= "(ATerm) ATmakeAppl0(ATmakeAFun((char *) e$n, 0, ATtrue))";
+#                $type = "const char *";
+                $type = "ATerm";
+                $args .= "e$n";
+                # !!! in the matcher, we should check that the
+                # argument is a string (i.e., a nullary application).
+            } elsif ($type eq "int") {
+                $args .= "(ATerm) ATmakeInt(e$n)";
+            } elsif ($type eq "ATermList" || $type eq "ATermBlob") {
+                $args .= "(ATerm) e$n";
+            } else {
+                $args .= "e$n";
+            }
+            $formals .= ", " if $formals ne "";
+            $formals .= "$type e$n";
+            $formals2 .= ", ";
+            $formals2 .= "$type & e$n";
+            my $m = $n - 1;
+            # !!! more checks here
+            if ($type eq "int") {
+                $unpack .= "    e$n = ATgetInt((ATermInt) ATgetArgument(e, $m));\n";
+            } elsif ($type eq "ATermList") {
+                $unpack .= "    e$n = (ATermList) ATgetArgument(e, $m);\n";
+            } elsif ($type eq "ATermBlob") {
+                $unpack .= "    e$n = (ATermBlob) ATgetArgument(e, $m);\n";
+            } elsif ($realType eq "string") {
+                $unpack .= "    e$n = ATgetArgument(e, $m);\n";
+                $unpack .= "    if (ATgetType(e$n) != AT_APPL) return false;\n";
+            } else {
+                $unpack .= "    e$n = ATgetArgument(e, $m);\n";
+            }
+            $n++;
+        }
+
+        my $arity = scalar @types;
+
+        print HEADER "extern AFun sym$funname;\n\n";
+        
+        print IMPL "AFun sym$funname = 0;\n";
+        
+        if ($arity == 0) {
+            print HEADER "extern ATerm const$funname;\n\n";
+            print IMPL "ATerm const$funname = 0;\n";
+        }
+        
+        print HEADER "static inline $result make$funname($formals) __attribute__ ((pure, nothrow));\n";
+        print HEADER "static inline $result make$funname($formals) {\n";
+        if ($arity == 0) {
+            print HEADER "    return const$funname;\n";
+        }
+        elsif ($arity <= 6) {
+            print HEADER "    return (ATerm) ATmakeAppl$arity(sym$funname$args);\n";
+        } else {
+            $args =~ s/^,//;
+            print HEADER "    ATerm array[$arity] = {$args};\n";
+            print HEADER "    return (ATerm) ATmakeApplArray(sym$funname, array);\n";
+        }
+        print HEADER "}\n\n";
+
+        print HEADER "#ifdef __cplusplus\n";
+        print HEADER "static inline bool match$funname(ATerm e$formals2) {\n";
+        print HEADER "    if (ATgetType(e) != AT_APPL || (AFun) ATgetAFun(e) != sym$funname) return false;\n";
+        print HEADER "$unpack";
+        print HEADER "    return true;\n";
+        print HEADER "}\n";
+        print HEADER "#endif\n\n\n";
+
+        $init .= "    sym$funname = ATmakeAFun(\"$const\", $arity, ATfalse);\n";
+        $init .= "    ATprotectAFun(sym$funname);\n";
+        if ($arity == 0) {
+            $init .= "    const$funname = (ATerm) ATmakeAppl0(sym$funname);\n";
+            $init .= "    ATprotect(&const$funname);\n";
+        }
+    }
+
+    elsif (/^\s*(\w+)\s*=\s*(.*)$/) {
+        my $name = $1;
+        my $value = $2;
+        print HEADER "extern ATerm $name;\n";
+        print IMPL "ATerm $name = 0;\n";
+        $init .= "    $name = $value;\n";
+    }
+
+    elsif (/^\s*init\s+(\w+)\s*$/) {
+        $initFun = $1;
+    }
+
+    else {
+        die "bad line: `$_'";
+    }
+}
+
+print HEADER "void $initFun();\n\n";
+
+print HEADER "static inline const char * aterm2String(ATerm t) {\n";
+print HEADER "    return (const char *) ATgetName(ATgetAFun(t));\n";
+print HEADER "}\n\n";
+
+print IMPL "\n";
+print IMPL "void $initFun() {\n";
+print IMPL "$init";
+print IMPL "}\n";
+
+print HEADER "#ifdef __cplusplus\n";
+print HEADER "}\n";
+print HEADER "#endif\n\n\n";
+print IMPL "}\n";
+
+close HEADER;
+close IMPL;
--- a/src/bin2c/Makefile.am
+++ b/src/bin2c/Makefile.am
@@ -1,6 +1,3 @@
 noinst_PROGRAMS = bin2c

 bin2c_SOURCES = bin2c.c
-
-bin2c$(EXEEXT): bin2c.c
-	$(CC_FOR_BUILD) $(CFLAGS_FOR_BUILD) -o bin2c bin2c.c
--- a/src/libexpr/Makefile.am
+++ b/src/libexpr/Makefile.am
@@ -2,25 +2,27 @@ pkglib_LTLIBRARIES = libexpr.la

 libexpr_la_SOURCES = \
 nixexpr.cc eval.cc primops.cc lexer-tab.cc parser-tab.cc \
- get-drvs.cc attr-path.cc value-to-xml.cc common-opts.cc \
- names.cc
+ get-drvs.cc attr-path.cc expr-to-xml.cc common-opts.cc \
+ names.cc normal-forms.cc

 pkginclude_HEADERS = \
 nixexpr.hh eval.hh parser.hh lexer-tab.hh parser-tab.hh \
- get-drvs.hh attr-path.hh value-to-xml.hh common-opts.hh \
- names.hh symbol-table.hh
+ get-drvs.hh attr-path.hh expr-to-xml.hh common-opts.hh \
+ names.hh nixexpr-ast.hh

 libexpr_la_LIBADD = ../libutil/libutil.la ../libstore/libstore.la \
 ../boost/format/libformat.la

-BUILT_SOURCES = \
+BUILT_SOURCES = nixexpr-ast.cc nixexpr-ast.hh \
 parser-tab.hh lexer-tab.hh parser-tab.cc lexer-tab.cc

-EXTRA_DIST = lexer.l parser.y
+EXTRA_DIST = lexer.l parser.y nixexpr-ast.def nixexpr-ast.cc

 AM_CXXFLAGS = \
- -I$(srcdir)/.. \
+ -I$(srcdir)/.. ${bdb_include} ${aterm_include} \
 -I$(srcdir)/../libutil -I$(srcdir)/../libstore
+AM_CFLAGS = \
+ ${aterm_include}


 # Parser generation.
@@ -32,6 +34,15 @@ lexer-tab.cc lexer-tab.hh: lexer.l
 	$(flex) --outfile lexer-tab.cc --header-file=lexer-tab.hh $(srcdir)/lexer.l 


+# ATerm helper function generation.
+
+nixexpr-ast.cc nixexpr-ast.hh: ../aterm-helper.pl nixexpr-ast.def
+	$(perl) $(srcdir)/../aterm-helper.pl nixexpr-ast.hh nixexpr-ast.cc < $(srcdir)/nixexpr-ast.def
+
+
+CLEANFILES =
+
+
 # SDF stuff (not built by default).
 nix.tbl: nix.sdf
 	sdf2table -m Nix -s -i nix.sdf -o nix.tbl
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -1,12 +1,23 @@
 #include "attr-path.hh"
+#include "nixexpr-ast.hh"
 #include "util.hh"


 namespace nix {


-void findAlongAttrPath(EvalState & state, const string & attrPath,
-    const Bindings & autoArgs, Expr * e, Value & v)
+bool isAttrs(EvalState & state, Expr e, ATermMap & attrs)
+{
+    e = evalExpr(state, e);
+    ATermList dummy;
+    if (!matchAttrs(e, dummy)) return false;
+    queryAllAttrs(e, attrs, false);
+    return true;
+}
+
+
+Expr findAlongAttrPath(EvalState & state, const string & attrPath,
+    const ATermMap & autoArgs, Expr e)
 {
    Strings tokens = tokenizeString(attrPath, ".");

@@ -14,10 +25,8 @@ void findAlongAttrPath(EvalState & state, const string & attrPath,
        Error(format("attribute selection path `%1%' does not match expression") % attrPath);

    string curPath;
-
-    state.mkThunk_(v, e);
    
-    foreach (Strings::iterator, i, tokens) {
+    for (Strings::iterator i = tokens.begin(); i != tokens.end(); ++i) {

        if (!curPath.empty()) curPath += ".";
        curPath += *i;
@@ -29,10 +38,7 @@ void findAlongAttrPath(EvalState & state, const string & attrPath,
        if (string2Int(attr, attrIndex)) apType = apIndex;

        /* Evaluate the expression. */
-        Value vTmp;
-        state.autoCallFunction(autoArgs, v, vTmp);
-        v = vTmp;
-        state.forceValue(v);
+        e = evalExpr(state, autoCallFunction(evalExpr(state, e), autoArgs));

        /* It should evaluate to either an attribute set or an
           expression, according to what is specified in the
@@ -40,31 +46,36 @@ void findAlongAttrPath(EvalState & state, const string & attrPath,

        if (apType == apAttr) {

-            if (v.type != tAttrs)
+            ATermMap attrs;
+
+            if (!isAttrs(state, e, attrs))
                throw TypeError(
                    format("the expression selected by the selection path `%1%' should be an attribute set but is %2%")
-                    % curPath % showType(v));
-
-            Bindings::iterator a = v.attrs->find(state.symbols.create(attr));
-            if (a == v.attrs->end())
+                    % curPath % showType(e));
+                
+            e = attrs.get(toATerm(attr));
+            if (!e)
                throw Error(format("attribute `%1%' in selection path `%2%' not found") % attr % curPath);
-            v = a->second.value;
+
        }

        else if (apType == apIndex) {

-            if (v.type != tList)
+            ATermList es;
+            if (!matchList(e, es))
                throw TypeError(
                    format("the expression selected by the selection path `%1%' should be a list but is %2%")
-                    % curPath % showType(v));
+                    % curPath % showType(e));

-            if (attrIndex >= v.list.length)
-                throw Error(format("list index %1% in selection path `%2%' is out of range") % attrIndex % curPath);
-
-            v = *v.list.elems[attrIndex];
+            e = ATelementAt(es, attrIndex);
+            if (!e)
+                throw Error(format("list index %1% in selection path `%2%' not found") % attrIndex % curPath);
+            
        }
        
    }
+    
+    return e;
 }

 
--- a/src/libexpr/attr-path.hh
+++ b/src/libexpr/attr-path.hh
@@ -10,8 +10,8 @@
 namespace nix {

    
-void findAlongAttrPath(EvalState & state, const string & attrPath,
-    const Bindings & autoArgs, Expr * e, Value & v);
+Expr findAlongAttrPath(EvalState & state, const string & attrPath,
+    const ATermMap & autoArgs, Expr e);

    
 }
--- a/src/libexpr/common-opts.cc
+++ b/src/libexpr/common-opts.cc
@@ -9,7 +9,7 @@ namespace nix {

 bool parseOptionArg(const string & arg, Strings::iterator & i,
    const Strings::iterator & argsEnd, EvalState & state,
-    Bindings & autoArgs)
+    ATermMap & autoArgs)
 {
    if (arg != "--arg" && arg != "--argstr") return false;

@@ -19,13 +19,11 @@ bool parseOptionArg(const string & arg, Strings::iterator & i,
    string name = *i++;
    if (i == argsEnd) throw error;
    string value = *i++;
-
-    Value & v(autoArgs[state.symbols.create(name)].value);
-
-    if (arg == "--arg")
-        state.mkThunk_( v, parseExprFromString(state, value, absPath(".")));
-    else
-        mkString(v, value);
+    
+    Expr e = arg == "--arg"
+        ? parseExprFromString(state, value, absPath("."))
+        : makeStr(value);
+    autoArgs.set(toATerm(name), e);
    
    return true;
 }
--- a/src/libexpr/common-opts.hh
+++ b/src/libexpr/common-opts.hh
@@ -9,7 +9,7 @@ namespace nix {
 /* Some common option parsing between nix-env and nix-instantiate. */
 bool parseOptionArg(const string & arg, Strings::iterator & i,
    const Strings::iterator & argsEnd, EvalState & state,
-    Bindings & autoArgs);
+    ATermMap & autoArgs);
    
 }

--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -3,165 +3,17 @@

 #include <map>

+#include "aterm.hh"
 #include "nixexpr.hh"
-#include "symbol-table.hh"


 namespace nix {


 class Hash;
-class EvalState;
-struct Env;
-struct Value;
-struct Attr;
-
-typedef std::map<Symbol, Attr> Bindings;
-
-
-typedef enum {
-    tInt = 1,
-    tBool,
-    tString,
-    tPath,
-    tNull,
-    tAttrs,
-    tList,
-    tThunk,
-    tApp,
-    tLambda,
-    tCopy,
-    tBlackhole,
-    tPrimOp,
-    tPrimOpApp,
-} ValueType;
-
-
-typedef void (* PrimOp) (EvalState & state, Value * * args, Value & v);
-
-
-struct Value
-{
-    ValueType type;
-    union 
-    {
-        int integer;
-        bool boolean;
-        
-        /* Strings in the evaluator carry a so-called `context' (the
-           ATermList) which is a list of strings representing store
-           paths.  This is to allow users to write things like
-
-             "--with-freetype2-library=" + freetype + "/lib"
-
-           where `freetype' is a derivation (or a source to be copied
-           to the store).  If we just concatenated the strings without
-           keeping track of the referenced store paths, then if the
-           string is used as a derivation attribute, the derivation
-           will not have the correct dependencies in its inputDrvs and
-           inputSrcs.
-
-           The semantics of the context is as follows: when a string
-           with context C is used as a derivation attribute, then the
-           derivations in C will be added to the inputDrvs of the
-           derivation, and the other store paths in C will be added to
-           the inputSrcs of the derivations.
-
-           For canonicity, the store paths should be in sorted order. */
-        struct {
-            const char * s;
-            const char * * context; // must be in sorted order
-        } string;
-        
-        const char * path;
-        Bindings * attrs;
-        struct {
-            unsigned int length;
-            Value * * elems;
-        } list;
-        struct {
-            Env * env;
-            Expr * expr;
-        } thunk;
-        struct {
-            Value * left, * right;
-        } app;
-        struct {
-            Env * env;
-            ExprLambda * fun;
-        } lambda;
-        Value * val;
-        struct {
-            PrimOp fun;
-            char * name;
-            unsigned int arity;
-        } primOp;
-        struct {
-            Value * left, * right;
-            unsigned int argsLeft;
-        } primOpApp;
-    };
-};
-
-
-struct Env
-{
-    Env * up;
-    unsigned int prevWith; // nr of levels up to next `with' environment
-    Value values[0];
-};
-
-
-struct Attr
-{
-    Value value;
-    Pos * pos;
-    Attr() : pos(&noPos) { };
-};
-
-
-static inline void mkInt(Value & v, int n)
-{
-    v.type = tInt;
-    v.integer = n;
-}
-
-
-static inline void mkBool(Value & v, bool b)
-{
-    v.type = tBool;
-    v.boolean = b;
-}
-
-
-static inline void mkThunk(Value & v, Env & env, Expr * expr)
-{
-    v.type = tThunk;
-    v.thunk.env = &env;
-    v.thunk.expr = expr;
-}
-
-
-static inline void mkCopy(Value & v, Value & src)
-{
-    v.type = tCopy;
-    v.val = &src;
-}
-
-
-static inline void mkApp(Value & v, Value & left, Value & right)
-{
-    v.type = tApp;
-    v.app.left = &left;
-    v.app.right = &right;
-}
-
-
-void mkString(Value & v, const char * s);
-void mkString(Value & v, const string & s, const PathSet & context = PathSet());
-void mkPath(Value & v, const char * s);
-
+    

+typedef std::map<Path, PathSet> DrvRoots;
 typedef std::map<Path, Hash> DrvHashes;

 /* Cache for calls to addToStore(); maps source paths to the store
@@ -170,153 +22,81 @@ typedef std::map<Path, Path> SrcToStore;

 struct EvalState;

-
-std::ostream & operator << (std::ostream & str, Value & v);
+/* Note: using a ATermVector is safe here, since when we call a primop
+   we also have an ATermList on the stack. */
+typedef Expr (* PrimOp) (EvalState &, const ATermVector & args);


-class EvalState 
+struct EvalState 
 {
-public:
+    ATermMap normalForms;
+    ATermMap sessionNormalForms;
+    ATermMap primOps;
+    DrvRoots drvRoots;
    DrvHashes drvHashes; /* normalised derivation hashes */
-
-    SymbolTable symbols;
-
-    const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sSystem;
-
-private:
    SrcToStore srcToStore; 

+    unsigned int nrEvaluated;
+    unsigned int nrCached;
+    unsigned int nrDepthAfterReset;
+
    bool allowUnsafeEquality;
+    bool safeCache;

-    std::map<Path, Expr *> parseTrees;
-
-public:
-    
    EvalState();
    ~EvalState();

-    /* Evaluate an expression read from the given file to normal
-       form. */
-    void evalFile(const Path & path, Value & v);
-
-    /* Evaluate an expression to normal form, storing the result in
-       value `v'. */
-    void eval(Expr * e, Value & v);
-    void eval(Env & env, Expr * e, Value & v);
-
-    /* Evaluation the expression, then verify that it has the expected
-       type. */
-    bool evalBool(Env & env, Expr * e);
-    void evalAttrs(Env & env, Expr * e, Value & v);
-
-    /* If `v' is a thunk, enter it and overwrite `v' with the result
-       of the evaluation of the thunk.  If `v' is a delayed function
-       application, call the function and overwrite `v' with the
-       result.  Otherwise, this is a no-op. */
-    void forceValue(Value & v);
-
-    /* Force a value, then recursively force list elements and
-       attributes. */
-    void strictForceValue(Value & v);
-
-    /* Force `v', and then verify that it has the expected type. */
-    int forceInt(Value & v);
-    bool forceBool(Value & v);
-    void forceAttrs(Value & v);
-    void forceList(Value & v);
-    void forceFunction(Value & v); // either lambda or primop
-    string forceString(Value & v);
-    string forceString(Value & v, PathSet & context);
-    string forceStringNoCtx(Value & v);
-
-    /* Return true iff the value `v' denotes a derivation (i.e. a
-       set with attribute `type = "derivation"'). */
-    bool isDerivation(Value & v);
-
-    /* String coercion.  Converts strings, paths and derivations to a
-       string.  If `coerceMore' is set, also converts nulls, integers,
-       booleans and lists to a string.  If `copyToStore' is set,
-       referenced paths are copied to the Nix store as a side effect.q */
-    string coerceToString(Value & v, PathSet & context,
-        bool coerceMore = false, bool copyToStore = true);
-
-    /* Path coercion.  Converts strings, paths and derivations to a
-       path.  The result is guaranteed to be a canonicalised, absolute
-       path.  Nothing is copied to the store. */
-    Path coerceToPath(Value & v, PathSet & context);
-
-private:
-
-    /* The base environment, containing the builtin functions and
-       values. */
-    Env & baseEnv;
-
-    unsigned int baseEnvDispl;
-
-public:
-    
-    /* The same, but used during parsing to resolve variables. */
-    StaticEnv staticBaseEnv; // !!! should be private
-
-private:
-    
-    void createBaseEnv();
-    
-    void addConstant(const string & name, Value & v);
-
+    void addPrimOps();
    void addPrimOp(const string & name,
        unsigned int arity, PrimOp primOp);
-
-    Value * lookupVar(Env * env, const VarRef & var);
-    
-    friend class ExprVar;
-    friend class ExprAttrs;
-    friend class ExprLet;
-
-public:
-    
-    /* Do a deep equality test between two values.  That is, list
-       elements and attributes are compared recursively. */
-    bool eqValues(Value & v1, Value & v2);
-
-    void callFunction(Value & fun, Value & arg, Value & v);
-
-    /* Automatically call a function for which each argument has a
-       default value or has a binding in the `args' map. */
-    void autoCallFunction(const Bindings & args, Value & fun, Value & res);
-    
-    /* Allocation primitives. */
-    Value * allocValues(unsigned int count);
-    Env & allocEnv(unsigned int size);
-
-    void mkList(Value & v, unsigned int length);
-    void mkAttrs(Value & v);
-    void mkThunk_(Value & v, Expr * expr);
-    
-    void cloneAttrs(Value & src, Value & dst);
-
-    /* Print statistics. */
-    void printStats();
-
-private:
-    
-    unsigned long nrEnvs;
-    unsigned long nrValuesInEnvs;
-    unsigned long nrValues;
-    unsigned long nrListElems;
-    unsigned long nrEvaluated;
-    unsigned int recursionDepth;
-    unsigned int maxRecursionDepth;
-    char * deepestStack; /* for measuring stack usage */
-    
-    friend class RecursionCounter;
+    void loadNormalForms();
+    void saveNormalForms();
 };


-/* Return a string representing the type of the value `v'. */
-string showType(const Value & v);
+/* Evaluate an expression to normal form. */
+Expr evalExpr(EvalState & state, Expr e);

+/* Evaluate an expression read from the given file to normal form. */
+Expr evalFile(EvalState & state, const Path & path);

+/* Evaluate an expression, and recursively evaluate list elements and
+   attributes.  If `canonicalise' is true, we remove things like
+   position information and make sure that attribute sets are in
+   sorded order. */
+Expr strictEvalExpr(EvalState & state, Expr e);
+
+/* Specific results. */
+string evalString(EvalState & state, Expr e, PathSet & context);
+string evalStringNoCtx(EvalState & state, Expr e);
+int evalInt(EvalState & state, Expr e);
+bool evalBool(EvalState & state, Expr e);
+ATermList evalList(EvalState & state, Expr e);
+
+/* Flatten nested lists into a single list (or expand a singleton into
+   a list). */
+ATermList flattenList(EvalState & state, Expr e);
+
+/* String coercion.  Converts strings, paths and derivations to a
+   string.  If `coerceMore' is set, also converts nulls, integers,
+   booleans and lists to a string. */
+string coerceToString(EvalState & state, Expr e, PathSet & context,
+    bool coerceMore = false, bool copyToStore = true);
+
+/* Path coercion.  Converts strings, paths and derivations to a path.
+   The result is guaranteed to be an canonicalised, absolute path.
+   Nothing is copied to the store. */
+Path coerceToPath(EvalState & state, Expr e, PathSet & context);
+
+/* Automatically call a function for which each argument has a default
+   value or has a binding in the `args' map.  Note: result is a call,
+   not a normal form; it should be evaluated by calling evalExpr(). */
+Expr autoCallFunction(Expr e, const ATermMap & args);
+
+/* Print statistics. */
+void printEvalStats(EvalState & state);
+
+ 
 }


--- a/src/libexpr/expr-to-xml.cc
+++ b/src/libexpr/expr-to-xml.cc
@@ -0,0 +1,156 @@
+#include "expr-to-xml.hh"
+#include "xml-writer.hh"
+#include "nixexpr-ast.hh"
+#include "aterm.hh"
+#include "util.hh"
+
+#include <cstdlib>
+
+
+namespace nix {
+
+    
+static XMLAttrs singletonAttrs(const string & name, const string & value)
+{
+    XMLAttrs attrs;
+    attrs[name] = value;
+    return attrs;
+}
+
+
+/* set<Expr> is safe because all the expressions are also reachable
+   from the stack, therefore can't be garbage-collected. */
+typedef set<Expr> ExprSet;
+
+
+static void printTermAsXML(Expr e, XMLWriter & doc, PathSet & context,
+    ExprSet & drvsSeen);
+
+
+static void showAttrs(const ATermMap & attrs, XMLWriter & doc,
+    PathSet & context, ExprSet & drvsSeen)
+{
+    StringSet names;
+    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
+        names.insert(aterm2String(i->key));
+    for (StringSet::iterator i = names.begin(); i != names.end(); ++i) {
+        XMLOpenElement _(doc, "attr", singletonAttrs("name", *i));
+        printTermAsXML(attrs.get(toATerm(*i)), doc, context, drvsSeen);
+    }
+}
+
+
+static void printPatternAsXML(Pattern pat, XMLWriter & doc)
+{
+    ATerm name;
+    ATermList formals;
+    Pattern pat1, pat2;
+    ATermBool ellipsis;
+    if (matchVarPat(pat, name))
+        doc.writeEmptyElement("varpat", singletonAttrs("name", aterm2String(name)));
+    else if (matchAttrsPat(pat, formals, ellipsis)) {
+        XMLOpenElement _(doc, "attrspat");
+        for (ATermIterator i(formals); i; ++i) {
+            Expr name; ATerm dummy;
+            if (!matchFormal(*i, name, dummy)) abort();
+            doc.writeEmptyElement("attr", singletonAttrs("name", aterm2String(name)));
+        }
+        if (ellipsis == eTrue) doc.writeEmptyElement("ellipsis");
+    }
+    else if (matchAtPat(pat, pat1, pat2)) {
+        XMLOpenElement _(doc, "at");
+        printPatternAsXML(pat1, doc);
+        printPatternAsXML(pat2, doc);
+    }
+}
+
+
+static void printTermAsXML(Expr e, XMLWriter & doc, PathSet & context,
+    ExprSet & drvsSeen)
+{
+    XMLAttrs attrs;
+    string s;
+    ATerm s2;
+    int i;
+    ATermList as, es;
+    ATerm pat, body, pos;
+
+    checkInterrupt();
+
+    if (matchStr(e, s, context)) /* !!! show the context? */
+        doc.writeEmptyElement("string", singletonAttrs("value", s));
+
+    else if (matchPath(e, s2))
+        doc.writeEmptyElement("path", singletonAttrs("value", aterm2String(s2)));
+
+    else if (matchNull(e))
+        doc.writeEmptyElement("null");
+
+    else if (matchInt(e, i))
+        doc.writeEmptyElement("int", singletonAttrs("value", (format("%1%") % i).str()));
+
+    else if (e == eTrue)
+        doc.writeEmptyElement("bool", singletonAttrs("value", "true"));
+
+    else if (e == eFalse)
+        doc.writeEmptyElement("bool", singletonAttrs("value", "false"));
+
+    else if (matchAttrs(e, as)) {
+        ATermMap attrs;
+        queryAllAttrs(e, attrs);
+
+        Expr a = attrs.get(toATerm("type"));
+        if (a && matchStr(a, s, context) && s == "derivation") {
+
+            XMLAttrs xmlAttrs;
+            Path outPath, drvPath;
+            
+            a = attrs.get(toATerm("drvPath"));
+            if (matchStr(a, drvPath, context))
+                xmlAttrs["drvPath"] = drvPath;
+        
+            a = attrs.get(toATerm("outPath"));
+            if (matchStr(a, outPath, context))
+                xmlAttrs["outPath"] = outPath;
+        
+            XMLOpenElement _(doc, "derivation", xmlAttrs);
+
+            if (drvsSeen.find(e) == drvsSeen.end()) {
+                drvsSeen.insert(e);
+                showAttrs(attrs, doc, context, drvsSeen);
+            } else
+                doc.writeEmptyElement("repeated");
+        }
+
+        else {
+            XMLOpenElement _(doc, "attrs");
+            showAttrs(attrs, doc, context, drvsSeen);
+        }
+    }
+
+    else if (matchList(e, es)) {
+        XMLOpenElement _(doc, "list");
+        for (ATermIterator i(es); i; ++i)
+            printTermAsXML(*i, doc, context, drvsSeen);
+    }
+
+    else if (matchFunction(e, pat, body, pos)) {
+        XMLOpenElement _(doc, "function");
+        printPatternAsXML(pat, doc);
+    }
+
+    else
+        doc.writeEmptyElement("unevaluated");
+}
+
+
+void printTermAsXML(Expr e, std::ostream & out, PathSet & context)
+{
+    XMLWriter doc(true, out);
+    XMLOpenElement root(doc, "expr");
+    ExprSet drvsSeen;    
+    printTermAsXML(e, doc, context, drvsSeen);
+}
+
+ 
+}
--- a/src/libexpr/expr-to-xml.hh
+++ b/src/libexpr/expr-to-xml.hh
@@ -0,0 +1,16 @@
+#ifndef __EXPR_TO_XML_H
+#define __EXPR_TO_XML_H
+
+#include <string>
+#include <map>
+
+#include "nixexpr.hh"
+#include "aterm.hh"
+
+namespace nix {
+
+void printTermAsXML(Expr e, std::ostream & out, PathSet & context);
+    
+}
+
+#endif /* !__EXPR_TO_XML_H */
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -1,4 +1,5 @@
 #include "get-drvs.hh"
+#include "nixexpr-ast.hh"
 #include "util.hh"


@@ -7,10 +8,17 @@ namespace nix {

 string DrvInfo::queryDrvPath(EvalState & state) const
 {
-    if (drvPath == "" && attrs) {
-        Bindings::iterator i = attrs->find(state.sDrvPath);
+    if (drvPath == "") {
+        Expr a = attrs->get(toATerm("drvPath"));
+
+        /* Backwards compatibility hack with user environments made by
+           Nix <= 0.10: these contain illegal Path("") expressions. */
+        ATerm t;
+        if (a && matchPath(evalExpr(state, a), t))
+            return aterm2String(t);
+        
        PathSet context;
-        (string &) drvPath = i != attrs->end() ? state.coerceToPath(i->second.value, context) : "";
+        (string &) drvPath = a ? coerceToPath(state, a, context) : "";
    }
    return drvPath;
 }
@@ -18,10 +26,11 @@ string DrvInfo::queryDrvPath(EvalState & state) const

 string DrvInfo::queryOutPath(EvalState & state) const
 {
-    if (outPath == "" && attrs) {
-        Bindings::iterator i = attrs->find(state.sOutPath);
+    if (outPath == "") {
+        Expr a = attrs->get(toATerm("outPath"));
+        if (!a) throw TypeError("output path missing");
        PathSet context;
-        (string &) outPath = i != attrs->end() ? state.coerceToPath(i->second.value, context) : "";
+        (string &) outPath = coerceToPath(state, a, context);
    }
    return outPath;
 }
@@ -29,30 +38,35 @@ string DrvInfo::queryOutPath(EvalState & state) const

 MetaInfo DrvInfo::queryMetaInfo(EvalState & state) const
 {
-    if (metaInfoRead) return meta;
+    MetaInfo meta;
    
-    (bool &) metaInfoRead = true;
-    
-    Bindings::iterator a = attrs->find(state.sMeta);
-    if (a == attrs->end()) return meta; /* fine, empty meta information */
+    Expr a = attrs->get(toATerm("meta"));
+    if (!a) return meta; /* fine, empty meta information */

-    state.forceAttrs(a->second.value);
+    ATermMap attrs2;
+    queryAllAttrs(evalExpr(state, a), attrs2);

-    foreach (Bindings::iterator, i, *a->second.value.attrs) {
+    for (ATermMap::const_iterator i = attrs2.begin(); i != attrs2.end(); ++i) {
+        Expr e = evalExpr(state, i->value);
+        string s;
+        PathSet context;
        MetaValue value;
-        state.forceValue(i->second.value);
-        if (i->second.value.type == tString) {
+        int n;
+        ATermList es;
+        if (matchStr(e, s, context)) {
            value.type = MetaValue::tpString;
-            value.stringValue = i->second.value.string.s;
-        } else if (i->second.value.type == tInt) {
+            value.stringValue = s;
+            meta[aterm2String(i->key)] = value;
+        } else if (matchInt(e, n)) {
            value.type = MetaValue::tpInt;
-            value.intValue = i->second.value.integer;
-        } else if (i->second.value.type == tList) {
+            value.intValue = n;
+            meta[aterm2String(i->key)] = value;
+        } else if (matchList(e, es)) {
            value.type = MetaValue::tpStrings;
-            for (unsigned int j = 0; j < i->second.value.list.length; ++j)
-                value.stringValues.push_back(state.forceStringNoCtx(*i->second.value.list.elems[j]));
-        } else continue;
-        ((MetaInfo &) meta)[i->first] = value;
+            for (ATermIterator j(es); j; ++j)
+                value.stringValues.push_back(evalStringNoCtx(state, *j));
+            meta[aterm2String(i->key)] = value;
+        }
    }

    return meta;
@@ -68,46 +82,73 @@ MetaValue DrvInfo::queryMetaInfo(EvalState & state, const string & name) const

 void DrvInfo::setMetaInfo(const MetaInfo & meta)
 {
-    metaInfoRead = true;
-    this->meta = meta;
+    ATermMap metaAttrs;
+    foreach (MetaInfo::const_iterator, i, meta) {
+        Expr e;
+        switch (i->second.type) {
+            case MetaValue::tpInt: e = makeInt(i->second.intValue); break;
+            case MetaValue::tpString: e = makeStr(i->second.stringValue); break;
+            case MetaValue::tpStrings: {
+                ATermList es = ATempty;
+                foreach (Strings::const_iterator, j, i->second.stringValues)
+                    es = ATinsert(es, makeStr(*j));
+                e = makeList(ATreverse(es));
+                break;
+            }
+            default: abort();
+        }
+        metaAttrs.set(toATerm(i->first), makeAttrRHS(e, makeNoPos()));
+    }
+    attrs->set(toATerm("meta"), makeAttrs(metaAttrs));
 }


-/* Cache for already considered attrsets. */
-typedef set<Bindings *> Done;
+/* Cache for already evaluated derivations.  Usually putting ATerms in
+   a STL container is unsafe (they're not scanning for GC roots), but
+   here it doesn't matter; everything in this set is reachable from
+   the stack as well. */
+typedef set<Expr> Exprs;


-/* Evaluate value `v'.  If it evaluates to an attribute set of type
-   `derivation', then put information about it in `drvs' (unless it's
-   already in `doneExprs').  The result boolean indicates whether it
-   makes sense for the caller to recursively search for derivations in
-   `v'. */
-static bool getDerivation(EvalState & state, Value & v,
-    const string & attrPath, DrvInfos & drvs, Done & done)
+/* Evaluate expression `e'.  If it evaluates to an attribute set of
+   type `derivation', then put information about it in `drvs' (unless
+   it's already in `doneExprs').  The result boolean indicates whether
+   it makes sense for the caller to recursively search for derivations
+   in `e'. */
+static bool getDerivation(EvalState & state, Expr e,
+    const string & attrPath, DrvInfos & drvs, Exprs & doneExprs)
 {
    try {
-        state.forceValue(v);
-        if (!state.isDerivation(v)) return true;
+        
+        ATermList es;
+        e = evalExpr(state, e);
+        if (!matchAttrs(e, es)) return true;
+
+        boost::shared_ptr<ATermMap> attrs(new ATermMap());
+        queryAllAttrs(e, *attrs, false);
+        
+        Expr a = attrs->get(toATerm("type"));
+        if (!a || evalStringNoCtx(state, a) != "derivation") return true;

        /* Remove spurious duplicates (e.g., an attribute set like
           `rec { x = derivation {...}; y = x;}'. */
-        if (done.find(v.attrs) != done.end()) return false;
-        done.insert(v.attrs);
+        if (doneExprs.find(e) != doneExprs.end()) return false;
+        doneExprs.insert(e);

        DrvInfo drv;
    
-        Bindings::iterator i = v.attrs->find(state.sName);
+        a = attrs->get(toATerm("name"));
        /* !!! We really would like to have a decent back trace here. */
-        if (i == v.attrs->end()) throw TypeError("derivation name missing");
-        drv.name = state.forceStringNoCtx(i->second.value);
+        if (!a) throw TypeError("derivation name missing");
+        drv.name = evalStringNoCtx(state, a);

-        i = v.attrs->find(state.sSystem);
-        if (i == v.attrs->end())
+        a = attrs->get(toATerm("system"));
+        if (!a)
            drv.system = "unknown";
        else
-            drv.system = state.forceStringNoCtx(i->second.value);
+            drv.system = evalStringNoCtx(state, a);

-        drv.attrs = v.attrs;
+        drv.attrs = attrs;

        drv.attrPath = attrPath;

@@ -120,11 +161,11 @@ static bool getDerivation(EvalState & state, Value & v,
 }


-bool getDerivation(EvalState & state, Value & v, DrvInfo & drv)
+bool getDerivation(EvalState & state, Expr e, DrvInfo & drv)
 {
-    Done done;
+    Exprs doneExprs;
    DrvInfos drvs;
-    getDerivation(state, v, "", drvs, done);
+    getDerivation(state, e, "", drvs, doneExprs);
    if (drvs.size() != 1) return false;
    drv = drvs.front();
    return true;
@@ -137,73 +178,83 @@ static string addToPath(const string & s1, const string & s2)
 }


-static void getDerivations(EvalState & state, Value & vIn,
-    const string & pathPrefix, const Bindings & autoArgs,
-    DrvInfos & drvs, Done & done)
+static void getDerivations(EvalState & state, Expr e,
+    const string & pathPrefix, const ATermMap & autoArgs,
+    DrvInfos & drvs, Exprs & doneExprs)
 {
-    Value v;
-    state.autoCallFunction(autoArgs, vIn, v);
-    
+    e = evalExpr(state, autoCallFunction(evalExpr(state, e), autoArgs));
+
    /* Process the expression. */
+    ATermList es;
    DrvInfo drv;

-    if (!getDerivation(state, v, pathPrefix, drvs, done)) ;
+    if (!getDerivation(state, e, pathPrefix, drvs, doneExprs))
+        return;

-    else if (v.type == tAttrs) {
+    if (matchAttrs(e, es)) {
+        ATermMap drvMap(ATgetLength(es));
+        queryAllAttrs(e, drvMap);

        /* !!! undocumented hackery to support combining channels in
           nix-env.cc. */
-        bool combineChannels = v.attrs->find(state.symbols.create("_combineChannels")) != v.attrs->end();
+        bool combineChannels = drvMap.get(toATerm("_combineChannels"));

        /* Consider the attributes in sorted order to get more
           deterministic behaviour in nix-env operations (e.g. when
           there are names clashes between derivations, the derivation
           bound to the attribute with the "lower" name should take
           precedence). */
-        typedef std::map<string, Symbol> SortedSymbols;
-        SortedSymbols attrs;
-        foreach (Bindings::iterator, i, *v.attrs)
-            attrs.insert(std::pair<string, Symbol>(i->first, i->first));
+        typedef std::map<string, Expr> AttrsSorted;
+        AttrsSorted attrsSorted;
+        foreach (ATermMap::const_iterator, i, drvMap)
+            attrsSorted[aterm2String(i->key)] = i->value;

-        foreach (SortedSymbols::iterator, i, attrs) {
+        foreach (AttrsSorted::iterator, i, attrsSorted) {
            startNest(nest, lvlDebug, format("evaluating attribute `%1%'") % i->first);
            string pathPrefix2 = addToPath(pathPrefix, i->first);
-            Value & v2((*v.attrs)[i->second].value);
            if (combineChannels)
-                getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
-            else if (getDerivation(state, v2, pathPrefix2, drvs, done)) {
+                getDerivations(state, i->second, pathPrefix2, autoArgs, drvs, doneExprs);
+            else if (getDerivation(state, i->second, pathPrefix2, drvs, doneExprs)) {
                /* If the value of this attribute is itself an
                   attribute set, should we recurse into it?  => Only
                   if it has a `recurseForDerivations = true'
                   attribute. */
-                if (v2.type == tAttrs) {
-                    Bindings::iterator j = v2.attrs->find(state.symbols.create("recurseForDerivations"));
-                    if (j != v2.attrs->end() && state.forceBool(j->second.value))
-                        getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done);
+                ATermList es;
+                Expr e = evalExpr(state, i->second), e2;
+                if (matchAttrs(e, es)) {
+                    ATermMap attrs(ATgetLength(es));
+                    queryAllAttrs(e, attrs, false);
+                    if (((e2 = attrs.get(toATerm("recurseForDerivations")))
+                            && evalBool(state, e2)))
+                        getDerivations(state, e, pathPrefix2, autoArgs, drvs, doneExprs);
                }
            }
        }
+        
+        return;
    }

-    else if (v.type == tList) {
-        for (unsigned int n = 0; n < v.list.length; ++n) {
+    if (matchList(e, es)) {
+        int n = 0;
+        for (ATermIterator i(es); i; ++i, ++n) {
            startNest(nest, lvlDebug,
                format("evaluating list element"));
            string pathPrefix2 = addToPath(pathPrefix, (format("%1%") % n).str());
-            if (getDerivation(state, *v.list.elems[n], pathPrefix2, drvs, done))
-                getDerivations(state, *v.list.elems[n], pathPrefix2, autoArgs, drvs, done);
+            if (getDerivation(state, *i, pathPrefix2, drvs, doneExprs))
+                getDerivations(state, *i, pathPrefix2, autoArgs, drvs, doneExprs);
        }
+        return;
    }

-    else throw TypeError("expression does not evaluate to a derivation (or a set or list of those)");
+    throw TypeError("expression does not evaluate to a derivation (or a set or list of those)");
 }


-void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
-    const Bindings & autoArgs, DrvInfos & drvs)
+void getDerivations(EvalState & state, Expr e, const string & pathPrefix,
+    const ATermMap & autoArgs, DrvInfos & drvs)
 {
-    Done done;
-    getDerivations(state, v, pathPrefix, autoArgs, drvs, done);
+    Exprs doneExprs;
+    getDerivations(state, e, pathPrefix, autoArgs, drvs, doneExprs);
 }

 
--- a/src/libexpr/get-drvs.hh
+++ b/src/libexpr/get-drvs.hh
@@ -29,19 +29,16 @@ struct DrvInfo
 private:
    string drvPath;
    string outPath;
-
-    bool metaInfoRead;
-    MetaInfo meta;
    
 public:
    string name;
    string attrPath; /* path towards the derivation */
    string system;

-    /* !!! make this private */
-    Bindings * attrs;
-
-    DrvInfo() : metaInfoRead(false), attrs(0) { };
+    /* !!! these should really be hidden, and setMetaInfo() should
+       make a copy since the ATermMap can be shared between multiple
+       DrvInfos. */
+    boost::shared_ptr<ATermMap> attrs;

    string queryDrvPath(EvalState & state) const;
    string queryOutPath(EvalState & state) const;
@@ -65,12 +62,13 @@ public:
 typedef list<DrvInfo> DrvInfos;


-/* If value `v' denotes a derivation, store information about the
-   derivation in `drv' and return true.  Otherwise, return false. */
-bool getDerivation(EvalState & state, Value & v, DrvInfo & drv);
+/* Evaluate expression `e'.  If it evaluates to a derivation, store
+   information about the derivation in `drv' and return true.
+   Otherwise, return false. */
+bool getDerivation(EvalState & state, Expr e, DrvInfo & drv);

-void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
-    const Bindings & autoArgs, DrvInfos & drvs);
+void getDerivations(EvalState & state, Expr e, const string & pathPrefix,
+    const ATermMap & autoArgs, DrvInfos & drvs);

 
 }
--- a/src/libexpr/lexer.l
+++ b/src/libexpr/lexer.l
@@ -8,7 +8,9 @@


 %{
+#include "aterm.hh"
 #include "nixexpr.hh"
+#include "nixexpr-ast.hh"
 #define BISON_HEADER_HACK
 #include "parser-tab.hh"

@@ -19,16 +21,13 @@ namespace nix {
    
 static void initLoc(YYLTYPE * loc)
 {
-    loc->first_line = loc->last_line = 1;
-    loc->first_column = loc->last_column = 1;
+    loc->first_line = 1;
+    loc->first_column = 1;
 }

    
 static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
 {
-    loc->first_line = loc->last_line;
-    loc->first_column = loc->last_column;
-
    while (len--) {
       switch (*s++) {
       case '\r':
@@ -36,17 +35,17 @@ static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
               s++;
           /* fall through */
       case '\n': 
-           ++loc->last_line;
-           loc->last_column = 1;
+           ++loc->first_line;
+           loc->first_column = 1;
           break;
       default:
-           ++loc->last_column;
+           ++loc->first_column;
       }
    }
 }


-static Expr * unescapeStr(const char * s)
+static Expr unescapeStr(const char * s)
 {
    string t;
    char c;
@@ -66,7 +65,7 @@ static Expr * unescapeStr(const char * s)
        }
        else t += c;
    }
-    return new ExprString(t);
+    return makeStr(toATerm(t), ATempty);
 }

 
@@ -106,20 +105,19 @@ inherit     { return INHERIT; }
 \/\/        { return UPDATE; }
 \+\+        { return CONCAT; }

-{ID}        { yylval->id = strdup(yytext); return ID; }
+{ID}        { yylval->t = toATerm(yytext); return ID; /* !!! alloc */ }
 {INT}       { int n = atoi(yytext); /* !!! overflow */
-              yylval->n = n;
+              yylval->t = ATmake("<int>", n);
              return INT;
            }

 \"          { BEGIN(STRING); return '"'; }
 <STRING>([^\$\"\\]|\$[^\{\"]|\\.)+ {
-              /* !!! Not quite right: we want a follow restriction on
-                 "$", it shouldn't be followed by a "{".  Right now
-                 "$\"" will be consumed as part of a string, rather
-                 than a "$" followed by the string terminator.
-                 Disallow "$\"" for now. */
-              yylval->e = unescapeStr(yytext);
+/* !!! Not quite right: we want a follow restriction on "$", it
+   shouldn't be followed by a "{".  Right now "$\"" will be consumed
+   as part of a string, rather than a "$" followed by the string
+   terminator.  Disallow "$\"" for now. */
+              yylval->t = unescapeStr(yytext); /* !!! alloc */ 
              return STR;
            }
 <STRING>\$\{  { BEGIN(INITIAL); return DOLLAR_CURLY; }
@@ -128,31 +126,31 @@ inherit     { return INHERIT; }

 \'\'(\ *\n)?     { BEGIN(IND_STRING); return IND_STRING_OPEN; }
 <IND_STRING>([^\$\']|\$[^\{\']|\'[^\'\$])+ {
-                   yylval->e = new ExprIndStr(yytext);
+                   yylval->t = makeIndStr(toATerm(yytext));
                   return IND_STR;
                 }
 <IND_STRING>\'\'\$ {
-                   yylval->e = new ExprIndStr("$");
+                   yylval->t = makeIndStr(toATerm("$"));
                   return IND_STR;
                 }
 <IND_STRING>\'\'\' {
-                   yylval->e = new ExprIndStr("''");
+                   yylval->t = makeIndStr(toATerm("''"));
                   return IND_STR;
                 }
 <IND_STRING>\'\'\\. {
-                   yylval->e = unescapeStr(yytext + 2);
+                   yylval->t = unescapeStr(yytext + 2);
                   return IND_STR;
                 }
 <IND_STRING>\$\{ { BEGIN(INITIAL); return DOLLAR_CURLY; }
 <IND_STRING>\'\' { BEGIN(INITIAL); return IND_STRING_CLOSE; }
 <IND_STRING>\'   {
-                   yylval->e = new ExprIndStr("'");
+                   yylval->t = makeIndStr(toATerm("'"));
                   return IND_STR;
                 }
 <IND_STRING>.    return yytext[0]; /* just in case: shouldn't be reached */

-{PATH}      { yylval->path = strdup(yytext); return PATH; }
-{URI}       { yylval->uri = strdup(yytext); return URI; }
+{PATH}      { yylval->t = toATerm(yytext); return PATH; /* !!! alloc */ }
+{URI}       { yylval->t = toATerm(yytext); return URI; /* !!! alloc */ }

 [ \t\r\n]+    /* eat up whitespace */
 \#[^\r\n]*    /* single-line comments */
--- a/src/libexpr/nixexpr-ast.def
+++ b/src/libexpr/nixexpr-ast.def
@@ -0,0 +1,97 @@
+init initNixExprHelpers
+
+Pos | string int int | Pos |
+NoPos | | Pos |
+
+Function | Pattern Expr Pos | Expr |
+Assert | Expr Expr Pos | Expr |
+With | Expr Expr Pos | Expr |
+If | Expr Expr Expr | Expr |
+OpNot | Expr | Expr |
+OpEq | Expr Expr | Expr |
+OpNEq | Expr Expr | Expr |
+OpAnd | Expr Expr | Expr |
+OpOr | Expr Expr | Expr |
+OpImpl | Expr Expr | Expr |
+OpUpdate | Expr Expr | Expr |
+SubPath | Expr Expr | Expr |
+OpHasAttr | Expr string | Expr |
+OpPlus | Expr Expr | Expr |
+OpConcat | Expr Expr | Expr |
+ConcatStrings | ATermList | Expr |
+Call | Expr Expr | Expr |
+Select | Expr string | Expr |
+Var | string | Expr |
+Int | int | Expr |
+
+# Strings in the evaluator carry a so-called `context' (the ATermList)
+# which is a list of strings representing store paths.  This is to
+# allow users to write things like
+#
+#   "--with-freetype2-library=" + freetype + "/lib"
+#
+# where `freetype' is a derivation (or a source to be copied to the
+# store).  If we just concatenated the strings without keeping track
+# of the referenced store paths, then if the string is used as a
+# derivation attribute, the derivation will not have the correct
+# dependencies in its inputDrvs and inputSrcs.
+#
+# The semantics of the context is as follows: when a string with
+# context C is used as a derivation attribute, then the derivations in
+# C will be added to the inputDrvs of the derivation, and the other
+# store paths in C will be added to the inputSrcs of the derivations.
+#
+# For canonicity, the store paths should be in sorted order.
+Str | string ATermList | Expr |
+Str | string | Expr | ObsoleteStr
+
+# Internal to the parser, doesn't occur in ASTs.
+IndStr | string | Expr |
+
+# A path is a reference to a file system object that is to be copied
+# to the Nix store when used as a derivation attribute.  When it is
+# concatenated to a string (i.e., `str + path'), it is also copied and
+# the resulting store path is concatenated to the string (with the
+# store path in the context).  If a string or path is concatenated to
+# a path (i.e., `path + str' or `path + path'), the result is a new
+# path (if the right-hand side is a string, the context must be
+# empty).
+Path | string | Expr |
+
+List | ATermList | Expr |
+BlackHole | | Expr |
+Undefined | | Expr |
+Removed | | Expr |
+PrimOp | int ATermBlob ATermList | Expr |
+Attrs | ATermList | Expr |
+Closed | Expr | Expr |
+Rec | ATermList ATermList | Expr |
+Bool | ATermBool | Expr |
+Null | | Expr |
+
+Bind | string Expr Pos | ATerm |
+BindAttrPath | ATermList Expr Pos | ATerm | # desugared during parsing
+Bind | string Expr | ATerm | ObsoleteBind
+Inherit | Expr ATermList Pos | ATerm |
+
+Scope | | Expr |
+
+VarPat | string | Pattern |
+AttrsPat | ATermList ATermBool | Pattern | # bool = `...'
+AtPat | Pattern Pattern | Pattern |
+
+Formal | string DefaultValue | ATerm |
+
+DefaultValue | Expr | DefaultValue |
+NoDefaultValue | | DefaultValue |
+
+True | | ATermBool |
+False | | ATermBool |
+
+PrimOpDef | int ATermBlob | ATerm |
+
+AttrRHS | Expr Pos | ATerm |
+
+eTrue = makeBool(makeTrue())
+eFalse = makeBool(makeFalse())
+sOverrides = toATerm("__overrides")
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -1,325 +1,407 @@
 #include "nixexpr.hh"
 #include "derivations.hh"
 #include "util.hh"
+#include "aterm.hh"
+
+#include "nixexpr-ast.hh"
+#include "nixexpr-ast.cc"

 #include <cstdlib>


 namespace nix {
+    

-
-/* Displaying abstract syntax trees. */
-
-std::ostream & operator << (std::ostream & str, Expr & e)
+string showPos(ATerm pos)
 {
-    e.show(str);
-    return str;
+    ATerm path;
+    int line, column;
+    if (matchNoPos(pos)) return "undefined position";
+    if (!matchPos(pos, path, line, column))
+        throw badTerm("position expected", pos);
+    return (format("`%1%:%2%:%3%'") % aterm2String(path) % line % column).str();
 }
+    

-void Expr::show(std::ostream & str)
+ATerm bottomupRewrite(TermFun & f, ATerm e)
 {
-    abort();
-}
+    checkInterrupt();

-void ExprInt::show(std::ostream & str)
-{
-    str << n;
-}
+    if (ATgetType(e) == AT_APPL) {
+        AFun fun = ATgetAFun(e);
+        int arity = ATgetArity(fun);
+        ATerm args[arity];

-void ExprString::show(std::ostream & str)
-{
-    str << "\"" << s << "\""; // !!! escaping
-}
-
-void ExprPath::show(std::ostream & str)
-{
-    str << s;
-}
-
-void ExprVar::show(std::ostream & str)
-{
-    str << info.name;
-}
-
-void ExprSelect::show(std::ostream & str)
-{
-    str << "(" << *e << ")." << name;
-}
-
-void ExprOpHasAttr::show(std::ostream & str)
-{
-    str << "(" << *e << ") ? " << name;
-}
-
-void ExprAttrs::show(std::ostream & str)
-{
-    if (recursive) str << "rec ";
-    str << "{ ";
-    foreach (list<Inherited>::iterator, i, inherited)
-        str << "inherit " << i->first.name << "; ";
-    foreach (Attrs::iterator, i, attrs)
-        str << i->first << " = " << *i->second.first << "; ";
-    str << "}";
-}
-
-void ExprList::show(std::ostream & str)
-{
-    str << "[ ";
-    foreach (vector<Expr *>::iterator, i, elems)
-        str << "(" << **i << ") ";
-    str << "]";
-}
-
-void ExprLambda::show(std::ostream & str)
-{
-    str << "(";
-    if (matchAttrs) {
-        str << "{ ";
-        bool first = true;
-        foreach (Formals::Formals_::iterator, i, formals->formals) {
-            if (first) first = false; else str << ", ";
-            str << i->name;
-            if (i->def) str << " ? " << *i->def;
-        }
-        str << " }";
-        if (!arg.empty()) str << " @ ";
+        for (int i = 0; i < arity; ++i)
+            args[i] = bottomupRewrite(f, ATgetArgument(e, i));
+        
+        e = (ATerm) ATmakeApplArray(fun, args);
    }
-    if (!arg.empty()) str << arg;
-    str << ": " << *body << ")";
+
+    else if (ATgetType(e) == AT_LIST) {
+        ATermList in = (ATermList) e;
+        ATermList out = ATempty;
+
+        for (ATermIterator i(in); i; ++i)
+            out = ATinsert(out, bottomupRewrite(f, *i));
+
+        e = (ATerm) ATreverse(out);
+    }
+
+    return f(e);
 }

-void ExprLet::show(std::ostream & str)
-{
-    str << "let ";
-    foreach (list<ExprAttrs::Inherited>::iterator, i, attrs->inherited)
-        str << "inherit " << i->first.name << "; ";
-    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
-        str << i->first << " = " << *i->second.first << "; ";
-    str << "in " << *body;
-}

-void ExprWith::show(std::ostream & str)
+void queryAllAttrs(Expr e, ATermMap & attrs, bool withPos)
 {
-    str << "with " << *attrs << "; " << *body;
-}
+    ATermList bnds;
+    if (!matchAttrs(e, bnds))
+        throw TypeError(format("value is %1% while an attribute set was expected") % showType(e));

-void ExprIf::show(std::ostream & str)
-{
-    str << "if " << *cond << " then " << *then << " else " << *else_;
-}
-
-void ExprAssert::show(std::ostream & str)
-{
-    str << "assert " << *cond << "; " << *body;
-}
-
-void ExprOpNot::show(std::ostream & str)
-{
-    str << "! " << *e;
-}
-
-void ExprConcatStrings::show(std::ostream & str)
-{
-    bool first = true;
-    foreach (vector<Expr *>::iterator, i, *es) {
-        if (first) first = false; else str << " + ";
-        str << **i;
+    for (ATermIterator i(bnds); i; ++i) {
+        ATerm name;
+        Expr e;
+        ATerm pos;
+        if (!matchBind(*i, name, e, pos)) abort(); /* can't happen */
+        attrs.set(name, withPos ? makeAttrRHS(e, pos) : e);
    }
 }


-std::ostream & operator << (std::ostream & str, const Pos & pos)
+Expr queryAttr(Expr e, const string & name)
 {
-    if (!pos.line)
-        str << "undefined position";
-    else
-        str << (format("`%1%:%2%:%3%'") % pos.file % pos.line % pos.column).str();
-    return str;
+    ATerm dummy;
+    return queryAttr(e, name, dummy);
 }


-Pos noPos;
-
-
-/* Computing levels/displacements for variables. */
-
-void Expr::bindVars(const StaticEnv & env)
+Expr queryAttr(Expr e, const string & name, ATerm & pos)
 {
-    abort();
-}
+    ATermList bnds;
+    if (!matchAttrs(e, bnds))
+        throw TypeError(format("value is %1% while an attribute set was expected") % showType(e));

-void ExprInt::bindVars(const StaticEnv & env)
-{
-}
-
-void ExprString::bindVars(const StaticEnv & env)
-{
-}
-
-void ExprPath::bindVars(const StaticEnv & env)
-{
-}
-
-void VarRef::bind(const StaticEnv & env)
-{
-    /* Check whether the variable appears in the environment.  If so,
-       set its level and displacement. */
-    const StaticEnv * curEnv;
-    unsigned int level;
-    int withLevel = -1;
-    for (curEnv = &env, level = 0; curEnv; curEnv = curEnv->up, level++) {
-        if (curEnv->isWith) {
-            if (withLevel == -1) withLevel = level;
-        } else {
-            StaticEnv::Vars::const_iterator i = curEnv->vars.find(name);
-            if (i != curEnv->vars.end()) {
-                fromWith = false;
-                this->level = level;
-                displ = i->second;
-                return;
-            }
+    for (ATermIterator i(bnds); i; ++i) {
+        ATerm name2, pos2;
+        Expr e;
+        if (!matchBind(*i, name2, e, pos2))
+            abort(); /* can't happen */
+        if (aterm2String(name2) == name) {
+            pos = pos2;
+            return e;
        }
    }

-    /* Otherwise, the variable must be obtained from the nearest
-       enclosing `with'.  If there is no `with', then we can issue an
-       "undefined variable" error now. */
-    if (withLevel == -1) throw EvalError(format("undefined variable `%1%'") % name);
-
-    fromWith = true;
-    this->level = withLevel;
+    return 0;
 }

-void ExprVar::bindVars(const StaticEnv & env)
+
+Expr makeAttrs(const ATermMap & attrs)
 {
-    info.bind(env);
+    ATermList bnds = ATempty;
+    for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i) {
+        Expr e;
+        ATerm pos;
+        if (!matchAttrRHS(i->value, e, pos))
+            abort(); /* can't happen */
+        bnds = ATinsert(bnds, makeBind(i->key, e, pos));
+    }
+    return makeAttrs(bnds);
 }

-void ExprSelect::bindVars(const StaticEnv & env)
+
+static void varsBoundByPattern(ATermMap & map, Pattern pat)
 {
-    e->bindVars(env);
-}
-
-void ExprOpHasAttr::bindVars(const StaticEnv & env)
-{
-    e->bindVars(env);
-}
-
-void ExprAttrs::bindVars(const StaticEnv & env)
-{
-    if (recursive) {
-        StaticEnv newEnv(false, &env);
-    
-        unsigned int displ = 0;
-
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            newEnv.vars[i->first] = displ++;
-
-        foreach (list<Inherited>::iterator, i, inherited) {
-            newEnv.vars[i->first.name] = displ++;
-            i->first.bind(env);
+    ATerm name;
+    ATermList formals;
+    Pattern pat1, pat2;
+    ATermBool ellipsis;
+    /* Use makeRemoved() so that it can be used directly in
+       substitute(). */
+    if (matchVarPat(pat, name))
+        map.set(name, makeRemoved());
+    else if (matchAttrsPat(pat, formals, ellipsis)) { 
+        for (ATermIterator i(formals); i; ++i) {
+            ATerm d1;
+            if (!matchFormal(*i, name, d1)) abort();
+            map.set(name, makeRemoved());
        }
-
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            i->second.first->bindVars(newEnv);
    }
-
-    else {
-        foreach (ExprAttrs::Attrs::iterator, i, attrs)
-            i->second.first->bindVars(env);
-
-        foreach (list<Inherited>::iterator, i, inherited)
-            i->first.bind(env);
+    else if (matchAtPat(pat, pat1, pat2)) {
+        varsBoundByPattern(map, pat1);
+        varsBoundByPattern(map, pat2);
    }
+    else abort();
 }

-void ExprList::bindVars(const StaticEnv & env)
+
+Expr substitute(const Substitution & subs, Expr e)
 {
-    foreach (vector<Expr *>::iterator, i, elems)
-        (*i)->bindVars(env);
-}
+    checkInterrupt();

-void ExprLambda::bindVars(const StaticEnv & env)
-{
-    StaticEnv newEnv(false, &env);
-    
-    unsigned int displ = 0;
-    
-    if (!arg.empty()) newEnv.vars[arg] = displ++;
+    //if (subs.size() == 0) return e;

-    if (matchAttrs) {
-        foreach (Formals::Formals_::iterator, i, formals->formals)
-            newEnv.vars[i->name] = displ++;
+    ATerm name, pos, e2;

-        foreach (Formals::Formals_::iterator, i, formals->formals)
-            if (i->def) i->def->bindVars(newEnv);
+    /* As an optimisation, don't substitute in subterms known to be
+       closed. */
+    if (matchClosed(e, e2)) return e;
+
+    if (matchVar(e, name)) {
+        Expr sub = subs.lookup(name);
+        if (sub == makeRemoved()) sub = 0;
+        Expr wrapped;
+        /* Add a "closed" wrapper around terms that aren't already
+           closed.  The check is necessary to prevent repeated
+           wrapping, e.g., closed(closed(closed(...))), which kills
+           caching. */
+        return sub ? (matchClosed(sub, wrapped) ? sub : makeClosed(sub)) : e;
    }

-    body->bindVars(newEnv);
-}
-
-void ExprLet::bindVars(const StaticEnv & env)
-{
-    StaticEnv newEnv(false, &env);
-    
-    unsigned int displ = 0;
-
-    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
-        newEnv.vars[i->first] = displ++;
-
-    foreach (list<ExprAttrs::Inherited>::iterator, i, attrs->inherited) {
-        newEnv.vars[i->first.name] = displ++;
-        i->first.bind(env);
+    /* In case of a function, filter out all variables bound by this
+       function. */
+    Pattern pat;
+    ATerm body;
+    if (matchFunction(e, pat, body, pos)) {
+        ATermMap map(16);
+        varsBoundByPattern(map, pat);
+        Substitution subs2(&subs, &map);
+        return makeFunction(
+            (Pattern) substitute(subs2, (Expr) pat),
+            substitute(subs2, body), pos);
    }

-    foreach (ExprAttrs::Attrs::iterator, i, attrs->attrs)
-        i->second.first->bindVars(newEnv);
-    
-    body->bindVars(newEnv);
-}
+    /* Idem for a mutually recursive attribute set. */
+    ATermList rbnds, nrbnds;
+    if (matchRec(e, rbnds, nrbnds)) {
+        ATermMap map(ATgetLength(rbnds) + ATgetLength(nrbnds));
+        for (ATermIterator i(rbnds); i; ++i)
+            if (matchBind(*i, name, e2, pos)) map.set(name, makeRemoved());
+            else abort(); /* can't happen */
+        for (ATermIterator i(nrbnds); i; ++i)
+            if (matchBind(*i, name, e2, pos)) map.set(name, makeRemoved());
+            else abort(); /* can't happen */
+        return makeRec(
+            (ATermList) substitute(Substitution(&subs, &map), (ATerm) rbnds),
+            (ATermList) substitute(subs, (ATerm) nrbnds));
+    }

-void ExprWith::bindVars(const StaticEnv & env)
-{
-    /* Does this `with' have an enclosing `with'?  If so, record its
-       level so that `lookupVar' can look up variables in the previous
-       `with' if this one doesn't contain the desired attribute. */
-    const StaticEnv * curEnv;
-    unsigned int level;
-    prevWith = 0;
-    for (curEnv = &env, level = 1; curEnv; curEnv = curEnv->up, level++)
-        if (curEnv->isWith) {
-            prevWith = level;
-            break;
+    if (ATgetType(e) == AT_APPL) {
+        AFun fun = ATgetAFun(e);
+        int arity = ATgetArity(fun);
+        ATerm args[arity];
+        bool changed = false;
+
+        for (int i = 0; i < arity; ++i) {
+            ATerm arg = ATgetArgument(e, i);
+            args[i] = substitute(subs, arg);
+            if (args[i] != arg) changed = true;
        }
+        
+        return changed ? (ATerm) ATmakeApplArray(fun, args) : e;
+    }
+
+    if (ATgetType(e) == AT_LIST) {
+        unsigned int len = ATgetLength((ATermList) e);
+        ATerm es[len];
+        ATermIterator i((ATermList) e);
+        for (unsigned int j = 0; i; ++i, ++j)
+            es[j] = substitute(subs, *i);
+        ATermList out = ATempty;
+        for (unsigned int j = len; j; --j)
+            out = ATinsert(out, es[j - 1]);
+        return (ATerm) out;
+    }
+
+    return e;
+}
+
+
+/* We use memoisation to prevent exponential complexity on heavily
+   shared ATerms (remember, an ATerm is a graph, not a tree!).  Note
+   that using an STL set is fine here wrt to ATerm garbage collection
+   since all the ATerms in the set are already reachable from
+   somewhere else. */
+static void checkVarDefs2(set<Expr> & done, const ATermMap & defs, Expr e)
+{
+    if (done.find(e) != done.end()) return;
+    done.insert(e);
    
-    attrs->bindVars(env);    
-    StaticEnv newEnv(true, &env);
-    body->bindVars(newEnv);
+    ATerm name, pos, value;
+    ATerm with, body;
+    ATermList rbnds, nrbnds;
+    Pattern pat;
+
+    /* Closed terms don't have free variables, so we don't have to
+       check by definition. */
+    if (matchClosed(e, value)) return;
+    
+    else if (matchVar(e, name)) {
+        if (!defs.get(name))
+            throw EvalError(format("undefined variable `%1%'")
+                % aterm2String(name));
+    }
+
+    else if (matchFunction(e, pat, body, pos)) {
+        ATermMap defs2(defs);
+        varsBoundByPattern(defs2, pat);
+        set<Expr> done2;
+        checkVarDefs2(done2, defs2, pat);
+        checkVarDefs2(done2, defs2, body);
+    }
+        
+    else if (matchRec(e, rbnds, nrbnds)) {
+        checkVarDefs2(done, defs, (ATerm) nrbnds);
+        ATermMap defs2(defs);
+        for (ATermIterator i(rbnds); i; ++i) {
+            if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
+            defs2.set(name, (ATerm) ATempty);
+        }
+        for (ATermIterator i(nrbnds); i; ++i) {
+            if (!matchBind(*i, name, value, pos)) abort(); /* can't happen */
+            defs2.set(name, (ATerm) ATempty);
+        }
+        set<Expr> done2;
+        checkVarDefs2(done2, defs2, (ATerm) rbnds);
+    }
+
+    else if (matchWith(e, with, body, pos)) {
+        /* We can't check the body without evaluating the definitions
+           (which is an arbitrary expression), so we don't do that
+           here but only when actually evaluating the `with'. */
+        checkVarDefs2(done, defs, with);
+    }
+    
+    else if (ATgetType(e) == AT_APPL) {
+        int arity = ATgetArity(ATgetAFun(e));
+        for (int i = 0; i < arity; ++i)
+            checkVarDefs2(done, defs, ATgetArgument(e, i));
+    }
+
+    else if (ATgetType(e) == AT_LIST)
+        for (ATermIterator i((ATermList) e); i; ++i)
+            checkVarDefs2(done, defs, *i);
 }

-void ExprIf::bindVars(const StaticEnv & env)
+
+void checkVarDefs(const ATermMap & defs, Expr e)
 {
-    cond->bindVars(env);
-    then->bindVars(env);
-    else_->bindVars(env);
+    set<Expr> done;
+    checkVarDefs2(done, defs, e);
 }

-void ExprAssert::bindVars(const StaticEnv & env)
+
+struct Canonicalise : TermFun
 {
-    cond->bindVars(env);
-    body->bindVars(env);
-}
+    ATerm operator () (ATerm e)
+    {
+        /* Remove position info. */
+        ATerm path;
+        int line, column;
+        if (matchPos(e, path, line, column))
+            return makeNoPos();

-void ExprOpNot::bindVars(const StaticEnv & env)
+        /* Sort attribute sets. */
+        ATermList _;
+        if (matchAttrs(e, _)) {
+            ATermMap attrs;
+            queryAllAttrs(e, attrs);
+            StringSet names;
+            for (ATermMap::const_iterator i = attrs.begin(); i != attrs.end(); ++i)
+                names.insert(aterm2String(i->key));
+
+            ATermList attrs2 = ATempty;
+            for (StringSet::reverse_iterator i = names.rbegin(); i != names.rend(); ++i)
+                attrs2 = ATinsert(attrs2,
+                    makeBind(toATerm(*i), attrs.get(toATerm(*i)), makeNoPos()));
+
+            return makeAttrs(attrs2);
+        }
+        
+        return e;
+    }
+};
+
+
+Expr canonicaliseExpr(Expr e)
 {
-    e->bindVars(env);
+    Canonicalise canonicalise;
+    return bottomupRewrite(canonicalise, e);
 }

-void ExprConcatStrings::bindVars(const StaticEnv & env)
+
+Expr makeBool(bool b)
 {
-    foreach (vector<Expr *>::iterator, i, *es)
-        (*i)->bindVars(env);
+    return b ? eTrue : eFalse;
 }


+bool matchStr(Expr e, string & s, PathSet & context)
+{
+    ATermList l;
+    ATerm s_;
+
+    if (!matchStr(e, s_, l)) return false;
+
+    s = aterm2String(s_);
+
+    for (ATermIterator i(l); i; ++i)
+        context.insert(aterm2String(*i));
+
+    return true;
+}
+
+
+Expr makeStr(const string & s, const PathSet & context)
+{
+    return makeStr(toATerm(s), toATermList(context));
+}
+
+
+string showType(Expr e)
+{
+    ATerm t1, t2;
+    ATermList l1;
+    ATermBlob b1;
+    int i1;
+    Pattern p1;
+    if (matchStr(e, t1, l1)) return "a string";
+    if (matchPath(e, t1)) return "a path";
+    if (matchNull(e)) return "null";
+    if (matchInt(e, i1)) return "an integer";
+    if (matchBool(e, t1)) return "a boolean";
+    if (matchFunction(e, p1, t1, t2)) return "a function";
+    if (matchAttrs(e, l1)) return "an attribute set";
+    if (matchList(e, l1)) return "a list";
+    if (matchPrimOp(e, i1, b1, l1)) return "a partially applied built-in function";
+    return "an unknown type";
+}
+
+
+string showValue(Expr e)
+{
+    PathSet context;
+    string s;
+    ATerm s2;
+    int i;
+    if (matchStr(e, s, context)) {
+        string u;
+        for (string::iterator i = s.begin(); i != s.end(); ++i)
+            if (*i == '\"' || *i == '\\') u += "\\" + *i;
+            else if (*i == '\n') u += "\\n";
+            else if (*i == '\r') u += "\\r";
+            else if (*i == '\t') u += "\\t";
+            else u += *i;
+        return "\"" + u + "\"";
+    }
+    if (matchPath(e, s2)) return aterm2String(s2);
+    if (matchNull(e)) return "null";
+    if (matchInt(e, i)) return (format("%1%") % i).str();
+    if (e == eTrue) return "true";
+    if (e == eFalse) return "false";
+    /* !!! incomplete */
+    return "<unknown>";
+}
+
+ 
 }
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -3,7 +3,8 @@

 #include <map>

-#include "symbol-table.hh"
+#include "aterm-map.hh"
+#include "types.hh"


 namespace nix {
@@ -17,254 +18,105 @@ MakeError(Abort, EvalError)
 MakeError(TypeError, EvalError)


-/* Position objects. */
+/* Nix expressions are represented as ATerms.  The maximal sharing
+   property of the ATerm library allows us to implement caching of
+   normals forms efficiently. */
+typedef ATerm Expr;
+typedef ATerm DefaultValue;
+typedef ATerm Pos;
+typedef ATerm Pattern;
+typedef ATerm ATermBool;

-struct Pos
+
+/* A STL vector of ATerms.  Should be used with great care since it's
+   stored on the heap, and the elements are therefore not roots to the
+   ATerm garbage collector. */
+typedef vector<ATerm> ATermVector;
+
+
+/* A substitution is a linked list of ATermMaps that map names to
+   identifiers.  We use a list of ATermMaps rather than a single to
+   make it easy to grow or shrink a substitution when entering a
+   scope. */
+struct Substitution
 {
-    string file;
-    unsigned int line, column;
-    Pos() : line(0), column(0) { };
-    Pos(const string & file, unsigned int line, unsigned int column)
-        : file(file), line(line), column(column) { };
-};
+    ATermMap * map;
+    const Substitution * prev;

-extern Pos noPos;
-
-std::ostream & operator << (std::ostream & str, const Pos & pos);
-
-
-struct Env;
-struct Value;
-struct EvalState;
-struct StaticEnv;
-
-
-/* Abstract syntax of Nix expressions. */
-
-struct Expr
-{
-    virtual void show(std::ostream & str);
-    virtual void bindVars(const StaticEnv & env);
-    virtual void eval(EvalState & state, Env & env, Value & v);
-};
-
-std::ostream & operator << (std::ostream & str, Expr & e);
-
-#define COMMON_METHODS \
-    void show(std::ostream & str); \
-    void eval(EvalState & state, Env & env, Value & v); \
-    void bindVars(const StaticEnv & env);
-
-struct ExprInt : Expr
-{
-    int n;
-    ExprInt(int n) : n(n) { };
-    COMMON_METHODS
-};
-
-struct ExprString : Expr
-{
-    string s;
-    ExprString(const string & s) : s(s) { };
-    COMMON_METHODS
-};
-
-/* Temporary class used during parsing of indented strings. */
-struct ExprIndStr : Expr
-{
-    string s;
-    ExprIndStr(const string & s) : s(s) { };
-};
-
-struct ExprPath : Expr
-{
-    string s;
-    ExprPath(const string & s) : s(s) { };
-    COMMON_METHODS
-};
-
-struct VarRef
-{
-    Symbol name;
-
-    /* Whether the variable comes from an environment (e.g. a rec, let
-       or function argument) or from a "with". */
-    bool fromWith;
-    
-    /* In the former case, the value is obtained by going `level'
-       levels up from the current environment and getting the
-       `displ'th value in that environment.  In the latter case, the
-       value is obtained by getting the attribute named `name' from
-       the attribute set stored in the environment that is `level'
-       levels up from the current one.*/
-    unsigned int level;
-    unsigned int displ;
-
-    VarRef(const Symbol & name) : name(name) { };
-    void bind(const StaticEnv & env);
-};
-
-struct ExprVar : Expr
-{
-    VarRef info;
-    ExprVar(const Symbol & name) : info(name) { };
-    COMMON_METHODS
-};
-
-struct ExprSelect : Expr
-{
-    Expr * e;
-    Symbol name;
-    ExprSelect(Expr * e, const Symbol & name) : e(e), name(name) { };
-    COMMON_METHODS
-};
-
-struct ExprOpHasAttr : Expr
-{
-    Expr * e;
-    Symbol name;
-    ExprOpHasAttr(Expr * e, const Symbol & name) : e(e), name(name) { };
-    COMMON_METHODS
-};
-
-struct ExprAttrs : Expr
-{
-    bool recursive;
-    typedef std::pair<Expr *, Pos> Attr;
-    typedef std::pair<VarRef, Pos> Inherited;
-    typedef std::map<Symbol, Attr> Attrs;
-    Attrs attrs;
-    list<Inherited> inherited;
-    std::map<Symbol, Pos> attrNames; // used during parsing
-    ExprAttrs() : recursive(false) { };
-    COMMON_METHODS
-};
-
-struct ExprList : Expr
-{
-    std::vector<Expr *> elems;
-    ExprList() { };
-    COMMON_METHODS
-};
-
-struct Formal
-{
-    Symbol name;
-    Expr * def;
-    Formal(const Symbol & name, Expr * def) : name(name), def(def) { };
-};
-
-struct Formals
-{
-    typedef std::list<Formal> Formals_;
-    Formals_ formals;
-    std::set<Symbol> argNames; // used during parsing
-    bool ellipsis;
-};
-
-struct ExprLambda : Expr
-{
-    Pos pos;
-    Symbol arg;
-    bool matchAttrs;
-    Formals * formals;
-    Expr * body;
-    ExprLambda(const Pos & pos, const Symbol & arg, bool matchAttrs, Formals * formals, Expr * body)
-        : pos(pos), arg(arg), matchAttrs(matchAttrs), formals(formals), body(body)
+    Substitution(const Substitution * prev, ATermMap * map)
    {
-        if (!arg.empty() && formals && formals->argNames.find(arg) != formals->argNames.end())
-            throw ParseError(format("duplicate formal function argument `%1%' at %2%")
-                % arg % pos);
-    };
-    COMMON_METHODS
+        this->prev = prev;
+        this->map = map;
+    }
+    
+    Expr lookup(Expr name) const
+    {
+        Expr x;
+        for (const Substitution * s(this); s; s = s->prev)
+            if ((x = s->map->get(name))) return x;
+        return 0;
+    }
 };

-struct ExprLet : Expr
+
+/* Show a position. */
+string showPos(ATerm pos);
+
+/* Generic bottomup traversal over ATerms.  The traversal first
+   recursively descends into subterms, and then applies the given term
+   function to the resulting term. */
+struct TermFun
 {
-    ExprAttrs * attrs;
-    Expr * body;
-    ExprLet(ExprAttrs * attrs, Expr * body) : attrs(attrs), body(body) { };
-    COMMON_METHODS
-};
-
-struct ExprWith : Expr
-{
-    Pos pos;
-    Expr * attrs, * body;
-    unsigned int prevWith;
-    ExprWith(const Pos & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
-    COMMON_METHODS
-};
-
-struct ExprIf : Expr
-{
-    Expr * cond, * then, * else_;
-    ExprIf(Expr * cond, Expr * then, Expr * else_) : cond(cond), then(then), else_(else_) { };
-    COMMON_METHODS
-};
-
-struct ExprAssert : Expr
-{
-    Pos pos;
-    Expr * cond, * body;
-    ExprAssert(const Pos & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
-    COMMON_METHODS
-};
-
-struct ExprOpNot : Expr
-{
-    Expr * e;
-    ExprOpNot(Expr * e) : e(e) { };
-    COMMON_METHODS
-};
-
-#define MakeBinOp(name, s) \
-    struct Expr##name : Expr \
-    { \
-        Expr * e1, * e2; \
-        Expr##name(Expr * e1, Expr * e2) : e1(e1), e2(e2) { }; \
-        void show(std::ostream & str) \
-        { \
-            str << *e1 << " " s " " << *e2; \
-        } \
-        void bindVars(const StaticEnv & env) \
-        { \
-            e1->bindVars(env); e2->bindVars(env); \
-        } \
-        void eval(EvalState & state, Env & env, Value & v); \
-    };
-
-MakeBinOp(App, "")
-MakeBinOp(OpEq, "==")
-MakeBinOp(OpNEq, "!=")
-MakeBinOp(OpAnd, "&&")
-MakeBinOp(OpOr, "||")
-MakeBinOp(OpImpl, "->")
-MakeBinOp(OpUpdate, "//")
-MakeBinOp(OpConcatLists, "++")
-
-struct ExprConcatStrings : Expr
-{
-    vector<Expr *> * es;
-    ExprConcatStrings(vector<Expr *> * es) : es(es) { };
-    COMMON_METHODS
+    virtual ~TermFun() { }
+    virtual ATerm operator () (ATerm e) = 0;
 };
+ATerm bottomupRewrite(TermFun & f, ATerm e);


-/* Static environments are used to map variable names onto (level,
-   displacement) pairs used to obtain the value of the variable at
-   runtime. */
-struct StaticEnv
-{
-    bool isWith;
-    const StaticEnv * up;
-    typedef std::map<Symbol, unsigned int> Vars;
-    Vars vars;
-    StaticEnv(bool isWith, const StaticEnv * up) : isWith(isWith), up(up) { };
-};
+/* Query all attributes in an attribute set expression.  The
+   expression must be in normal form. */
+void queryAllAttrs(Expr e, ATermMap & attrs, bool withPos = false);
+
+/* Query a specific attribute from an attribute set expression.  The
+   expression must be in normal form. */
+Expr queryAttr(Expr e, const string & name);
+Expr queryAttr(Expr e, const string & name, ATerm & pos);
+
+/* Create an attribute set expression from an Attrs value. */
+Expr makeAttrs(const ATermMap & attrs);


+/* Perform a set of substitutions on an expression. */
+Expr substitute(const Substitution & subs, Expr e);

+
+/* Check whether all variables are defined in the given expression.
+   Throw an exception if this isn't the case. */
+void checkVarDefs(const ATermMap & def, Expr e);
+
+
+/* Canonicalise a Nix expression by sorting attributes and removing
+   location information. */
+Expr canonicaliseExpr(Expr e);
+
+
+/* Create an expression representing a boolean. */
+Expr makeBool(bool b);
+
+
+/* Manipulation of Str() nodes.  Note: matchStr() does not clear
+   context!  */
+bool matchStr(Expr e, string & s, PathSet & context);
+
+Expr makeStr(const string & s, const PathSet & context = PathSet());
+
+
+/* Showing types, values. */
+string showType(Expr e);
+
+string showValue(Expr e);
+
+ 
 }


--- a/src/libexpr/normal-forms.cc
+++ b/src/libexpr/normal-forms.cc
@@ -0,0 +1,64 @@
+#include "eval.hh"
+#include "util.hh"
+#include "globals.hh"
+#include "serialise.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+namespace nix {
+
+
+void EvalState::loadNormalForms()
+{
+    //    nixCacheFile = getEnv("NIX_CACHE_FILE", nixStateDir + "/reduce-cache");
+    nixCacheFile = getEnv("NIX_CACHE_FILE");
+    string loadFlag = getEnv("NIX_CACHE_FILE_LOAD", "1");
+
+    if(nixCacheFile == "" || loadFlag == "")
+        return;
+    if(!pathExists(nixCacheFile))
+        return;
+
+    printMsg(lvlInfo, format("Load cache: ..."));
+    try {
+        int fd = open(nixCacheFile.c_str(), O_RDONLY);
+        if (fd == -1)
+            throw SysError(format("opening file `%1%'") % nixCacheFile);
+        AutoCloseFD auto_fd = fd;
+
+        FdSource source = fd;
+        normalForms = readATermMap(source);
+    } catch (Error & e) {
+        e.addPrefix(format("Cannot load cached reduce operations from %1%:\n") % nixCacheFile);
+        throw;
+    }
+    printMsg(lvlInfo, format("Load cache: end"));
+}
+
+void EvalState::saveNormalForms()
+{
+    string saveFlag = getEnv("NIX_CACHE_FILE_SAVE", "");
+
+    if(nixCacheFile == "" || saveFlag == "")
+        return;
+
+    printMsg(lvlInfo, format("Save cache: ..."));
+    try {
+        int fd = open(nixCacheFile.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
+        if (fd == -1)
+            throw SysError(format("opening file `%1%'") % nixCacheFile);
+        AutoCloseFD auto_fd = fd;
+
+        FdSink sink = fd;
+        writeATermMap(normalForms, sink);
+    } catch (Error & e) {
+        e.addPrefix(format("Cannot save cached reduce operations to %1%:\n") % nixCacheFile);
+        throw;
+    }
+    printMsg(lvlInfo, format("Save cache: end"));
+}
+
+
+}
--- a/src/libexpr/parser.hh
+++ b/src/libexpr/parser.hh
@@ -8,11 +8,12 @@ namespace nix {


 /* Parse a Nix expression from the specified file.  If `path' refers
-   to a directory, then "/default.nix" is appended. */
-Expr * parseExprFromFile(EvalState & state, Path path);
+   to a directory, the "/default.nix" is appended. */
+Expr parseExprFromFile(EvalState & state, Path path);

 /* Parse a Nix expression from the specified string. */
-Expr * parseExprFromString(EvalState & state, const string & s, const Path & basePath);
+Expr parseExprFromString(EvalState & state, const string & s,
+    const Path & basePath);


 }
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -20,14 +20,16 @@
 #include <stdlib.h>
 #include <string.h>

+#include "aterm.hh"
 #include "util.hh"
    
-#include "nixexpr.hh"
-
 #include "parser-tab.hh"
 #include "lexer-tab.hh"
 #define YYSTYPE YYSTYPE // workaround a bug in Bison 2.4

+#include "nixexpr.hh"
+#include "nixexpr-ast.hh"
+

 using namespace nix;

@@ -37,85 +39,139 @@ namespace nix {
    
 struct ParseData 
 {
-    SymbolTable & symbols;
-    Expr * result;
+    Expr result;
    Path basePath;
    Path path;
    string error;
-    Symbol sLetBody;
-    ParseData(SymbolTable & symbols)
-        : symbols(symbols)
-        , sLetBody(symbols.create("<let-body>"))
-    { };
 };
+ 

-
-static string showAttrPath(const vector<Symbol> & attrPath)
+static string showAttrPath(ATermList attrPath)
 {
    string s;
-    foreach (vector<Symbol>::const_iterator, i, attrPath) {
+    for (ATermIterator i(attrPath); i; ++i) {
        if (!s.empty()) s += '.';
-        s += *i;
+        s += aterm2String(*i);
    }
    return s;
 }
+ 

-
-static void dupAttr(const vector<Symbol> & attrPath, const Pos & pos, const Pos & prevPos)
+struct Tree
 {
-    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
-        % showAttrPath(attrPath) % pos % prevPos);
+    Expr leaf; ATerm pos; bool recursive;
+    typedef std::map<ATerm, Tree> Children;
+    Children children;
+    Tree() { leaf = 0; recursive = true; }
+};
+
+
+static ATermList buildAttrs(const Tree & t, ATermList & nonrec)
+{
+    ATermList res = ATempty;
+    for (Tree::Children::const_reverse_iterator i = t.children.rbegin();
+         i != t.children.rend(); ++i)
+        if (!i->second.recursive)
+            nonrec = ATinsert(nonrec, makeBind(i->first, i->second.leaf, i->second.pos));
+        else
+            res = ATinsert(res, i->second.leaf
+                ? makeBind(i->first, i->second.leaf, i->second.pos)
+                : makeBind(i->first, makeAttrs(buildAttrs(i->second, nonrec)), makeNoPos()));
+    return res;
 }
 

-static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
+static Expr fixAttrs(bool recursive, ATermList as)
 {
-    vector<Symbol> attrPath; attrPath.push_back(attr);
-    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
-        % showAttrPath(attrPath) % pos % prevPos);
-}
- 
+    Tree attrs;

-static void addAttr(ExprAttrs * attrs, const vector<Symbol> & attrPath,
-    Expr * e, const Pos & pos)
-{
-    unsigned int n = 0;
-    foreach (vector<Symbol>::const_iterator, i, attrPath) {
-        n++;
-        ExprAttrs::Attrs::iterator j = attrs->attrs.find(*i);
-        if (j != attrs->attrs.end()) {
-            ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.first);
-            if (!attrs2 || n == attrPath.size()) dupAttr(attrPath, pos, j->second.second);
-            attrs = attrs2;
-        } else {
-            if (attrs->attrNames.find(*i) != attrs->attrNames.end())
-                dupAttr(attrPath, pos, attrs->attrNames[*i]);
-            attrs->attrNames[*i] = pos;
-            if (n == attrPath.size())
-                attrs->attrs[*i] = ExprAttrs::Attr(e, pos);
-            else {
-                ExprAttrs * nested = new ExprAttrs;
-                attrs->attrs[*i] = ExprAttrs::Attr(nested, pos);
-                attrs = nested;
+    for (ATermIterator i(as); i; ++i) {
+        ATermList names, attrPath; Expr src, e; ATerm name, pos;
+
+        if (matchInherit(*i, src, names, pos)) {
+            bool fromScope = matchScope(src);
+            for (ATermIterator j(names); j; ++j) {
+                if (attrs.children.find(*j) != attrs.children.end()) 
+                    throw ParseError(format("duplicate definition of attribute `%1%' at %2%")
+                        % showAttrPath(ATmakeList1(*j)) % showPos(pos));
+                Tree & t(attrs.children[*j]);
+                t.leaf = fromScope ? makeVar(*j) : makeSelect(src, *j);
+                t.pos = pos;
+                if (recursive && fromScope) t.recursive = false;
            }
        }
+
+        else if (matchBindAttrPath(*i, attrPath, e, pos)) {
+
+            Tree * t(&attrs);
+            
+            for (ATermIterator j(attrPath); j; ) {
+                name = *j; ++j;
+                if (t->leaf) throw ParseError(format("attribute set containing `%1%' at %2% already defined at %3%")
+                    % showAttrPath(attrPath) % showPos(pos) % showPos (t->pos));
+                t = &(t->children[name]);
+            }
+
+            if (t->leaf)
+                throw ParseError(format("duplicate definition of attribute `%1%' at %2% and %3%")
+                    % showAttrPath(attrPath) % showPos(pos) % showPos (t->pos));
+            if (!t->children.empty())
+                throw ParseError(format("duplicate definition of attribute `%1%' at %2%")
+                    % showAttrPath(attrPath) % showPos(pos));
+
+            t->leaf = e; t->pos = pos;
+        }
+
+        else abort(); /* can't happen */
    }
+
+    ATermList nonrec = ATempty;
+    ATermList rec = buildAttrs(attrs, nonrec);
+        
+    return recursive ? makeRec(rec, nonrec) : makeAttrs(rec);
 }


-static void addFormal(const Pos & pos, Formals * formals, const Formal & formal)
+static void checkPatternVars(ATerm pos, ATermMap & map, Pattern pat)
 {
-    if (formals->argNames.find(formal.name) != formals->argNames.end())
-        throw ParseError(format("duplicate formal function argument `%1%' at %2%")
-            % formal.name % pos);
-    formals->formals.push_front(formal);
-    formals->argNames.insert(formal.name);
+    ATerm name;
+    ATermList formals;
+    Pattern pat1, pat2;
+    ATermBool ellipsis;
+    if (matchVarPat(pat, name)) {
+        if (map.get(name))
+            throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+                % aterm2String(name) % showPos(pos));
+        map.set(name, name);
+    }
+    else if (matchAttrsPat(pat, formals, ellipsis)) { 
+        for (ATermIterator i(formals); i; ++i) {
+            ATerm d1;
+            if (!matchFormal(*i, name, d1)) abort();
+            if (map.get(name))
+                throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+                    % aterm2String(name) % showPos(pos));
+            map.set(name, name);
+        }
+    }
+    else if (matchAtPat(pat, pat1, pat2)) {
+        checkPatternVars(pos, map, pat1);
+        checkPatternVars(pos, map, pat2);
+    }
+    else abort();
 }


-static Expr * stripIndentation(vector<Expr *> & es)
+static void checkPatternVars(ATerm pos, Pattern pat)
 {
-    if (es.empty()) return new ExprString("");
+    ATermMap map;
+    checkPatternVars(pos, map, pat);
+}
+
+
+static Expr stripIndentation(ATermList es)
+{
+    if (es == ATempty) return makeStr("");
    
    /* Figure out the minimum indentation.  Note that by design
       whitespace-only final lines are not taken into account.  (So
@@ -123,9 +179,9 @@ static Expr * stripIndentation(vector<Expr *> & es)
    bool atStartOfLine = true; /* = seen only whitespace in the current line */
    unsigned int minIndent = 1000000;
    unsigned int curIndent = 0;
-    foreach (vector<Expr *>::iterator, i, es) {
-        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
-        if (!e) {
+    ATerm e;
+    for (ATermIterator i(es); i; ++i) {
+        if (!matchIndStr(*i, e)) {
            /* Anti-quotations end the current start-of-line whitespace. */
            if (atStartOfLine) {
                atStartOfLine = false;
@@ -133,11 +189,12 @@ static Expr * stripIndentation(vector<Expr *> & es)
            }
            continue;
        }
-        for (unsigned int j = 0; j < e->s.size(); ++j) {
+        string s = aterm2String(e);
+        for (unsigned int j = 0; j < s.size(); ++j) {
            if (atStartOfLine) {
-                if (e->s[j] == ' ')
+                if (s[j] == ' ')
                    curIndent++;
-                else if (e->s[j] == '\n') {
+                else if (s[j] == '\n') {
                    /* Empty line, doesn't influence minimum
                       indentation. */
                    curIndent = 0;
@@ -145,7 +202,7 @@ static Expr * stripIndentation(vector<Expr *> & es)
                    atStartOfLine = false;
                    if (curIndent < minIndent) minIndent = curIndent;
                }
-            } else if (e->s[j] == '\n') {
+            } else if (s[j] == '\n') {
                atStartOfLine = true;
                curIndent = 0;
            }
@@ -153,37 +210,37 @@ static Expr * stripIndentation(vector<Expr *> & es)
    }

    /* Strip spaces from each line. */
-    vector<Expr *> * es2 = new vector<Expr *>;
+    ATermList es2 = ATempty;
    atStartOfLine = true;
    unsigned int curDropped = 0;
-    unsigned int n = es.size();
-    for (vector<Expr *>::iterator i = es.begin(); i != es.end(); ++i, --n) {
-        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
-        if (!e) {
+    unsigned int n = ATgetLength(es);
+    for (ATermIterator i(es); i; ++i, --n) {
+        if (!matchIndStr(*i, e)) {
            atStartOfLine = false;
            curDropped = 0;
-            es2->push_back(*i);
+            es2 = ATinsert(es2, *i);
            continue;
        }
        
+        string s = aterm2String(e);
        string s2;
-        for (unsigned int j = 0; j < e->s.size(); ++j) {
+        for (unsigned int j = 0; j < s.size(); ++j) {
            if (atStartOfLine) {
-                if (e->s[j] == ' ') {
+                if (s[j] == ' ') {
                    if (curDropped++ >= minIndent)
-                        s2 += e->s[j];
+                        s2 += s[j];
                }
-                else if (e->s[j] == '\n') {
+                else if (s[j] == '\n') {
                    curDropped = 0;
-                    s2 += e->s[j];
+                    s2 += s[j];
                } else {
                    atStartOfLine = false;
                    curDropped = 0;
-                    s2 += e->s[j];
+                    s2 += s[j];
                }
            } else {
-                s2 += e->s[j];
-                if (e->s[j] == '\n') atStartOfLine = true;
+                s2 += s[j];
+                if (s[j] == '\n') atStartOfLine = true;
            }
        }

@@ -194,11 +251,11 @@ static Expr * stripIndentation(vector<Expr *> & es)
            if (p != string::npos && s2.find_first_not_of(' ', p + 1) == string::npos)
                s2 = string(s2, 0, p + 1);
        }
-
-        es2->push_back(new ExprString(s2));
+            
+        es2 = ATinsert(es2, makeStr(s2));
    }

-    return new ExprConcatStrings(es2);
+    return makeConcatStrings(ATreverse(es2));
 }


@@ -206,12 +263,13 @@ void backToString(yyscan_t scanner);
 void backToIndString(yyscan_t scanner);


-static Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
+static Pos makeCurPos(YYLTYPE * loc, ParseData * data)
 {
-    return Pos(data->path, loc.first_line, loc.first_column);
+    return makePos(toATerm(data->path),
+        loc->first_line, loc->first_column);
 }

-#define CUR_POS makeCurPos(*yylocp, data)
+#define CUR_POS makeCurPos(yylocp, data)


 }
@@ -219,43 +277,50 @@ static Pos makeCurPos(const YYLTYPE & loc, ParseData * data)

 void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * error)
 {
-    data->error = (format("%1%, at %2%")
-        % error % makeCurPos(*loc, data)).str();
+    data->error = (format("%1%, at `%2%':%3%:%4%")
+        % error % data->path % loc->first_line % loc->first_column).str();
 }


+/* Make sure that the parse stack is scanned by the ATerm garbage
+   collector. */
+static void * mallocAndProtect(size_t size)
+{
+    void * p = malloc(size);
+    if (p) ATprotectMemory(p, size);
+    return p;
+}
+
+static void freeAndUnprotect(void * p)
+{
+    ATunprotectMemory(p);
+    free(p);
+}
+
+#define YYMALLOC mallocAndProtect
+#define YYFREE freeAndUnprotect
+
+
 #endif


 %}

 %union {
-  nix::Expr * e;
-  nix::ExprList * list;
-  nix::ExprAttrs * attrs;
-  nix::Formals * formals;
-  nix::Formal * formal;
-  int n;
-  char * id; // !!! -> Symbol
-  char * path;
-  char * uri;
-  std::vector<nix::Symbol> * ids;
-  std::vector<nix::Expr *> * string_parts;
+  ATerm t;
+  ATermList ts;
+  struct {
+    ATermList formals;
+    bool ellipsis;
+  } formals;
 }

-%type <e> start expr expr_function expr_if expr_op
-%type <e> expr_app expr_select expr_simple
-%type <list> expr_list
-%type <attrs> binds
+%type <t> start expr expr_function expr_if expr_op
+%type <t> expr_app expr_select expr_simple bind inheritsrc formal
+%type <t> pattern pattern2
+%type <ts> binds ids attrpath expr_list string_parts ind_string_parts
 %type <formals> formals
-%type <formal> formal
-%type <ids> ids attrpath
-%type <string_parts> string_parts ind_string_parts
-%token <id> ID ATTRPATH
-%token <e> STR IND_STR
-%token <n> INT
-%token <path> PATH
-%token <uri> URI
+%token <t> ID INT STR IND_STR PATH URI
 %token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL
 %token DOLLAR_CURLY /* == ${ */
 %token IND_STRING_OPEN IND_STRING_CLOSE
@@ -279,172 +344,163 @@ start: expr { data->result = $1; };
 expr: expr_function;

 expr_function
-  : ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), false, 0, $3); }
-  | '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), true, $2, $5); }
-  | '{' formals '}' '@' ID ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), true, $2, $7); }
-  | ID '@' '{' formals '}' ':' expr_function
-    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), true, $4, $7); }
+  : pattern ':' expr_function
+    { checkPatternVars(CUR_POS, $1); $$ = makeFunction($1, $3, CUR_POS); }
  | ASSERT expr ';' expr_function
-    { $$ = new ExprAssert(CUR_POS, $2, $4); }
+    { $$ = makeAssert($2, $4, CUR_POS); }
  | WITH expr ';' expr_function
-    { $$ = new ExprWith(CUR_POS, $2, $4); }
+    { $$ = makeWith($2, $4, CUR_POS); }
  | LET binds IN expr_function
-    { $$ = new ExprLet($2, $4); }
+    { $$ = makeSelect(fixAttrs(true, ATinsert($2, makeBindAttrPath(ATmakeList1(toATerm("<let-body>")), $4, CUR_POS))), toATerm("<let-body>")); }
  | expr_if
  ;

 expr_if
-  : IF expr THEN expr ELSE expr { $$ = new ExprIf($2, $4, $6); }
+  : IF expr THEN expr ELSE expr
+    { $$ = makeIf($2, $4, $6); }
  | expr_op
  ;

 expr_op
-  : '!' expr_op %prec NEG { $$ = new ExprOpNot($2); }
-  | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
-  | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op AND expr_op { $$ = new ExprOpAnd($1, $3); }
-  | expr_op OR expr_op { $$ = new ExprOpOr($1, $3); }
-  | expr_op IMPL expr_op { $$ = new ExprOpImpl($1, $3); }
-  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate($1, $3); }
-  | expr_op '?' ID { $$ = new ExprOpHasAttr($1, data->symbols.create($3)); }
-  | expr_op '+' expr_op
-    { vector<Expr *> * l = new vector<Expr *>;
-      l->push_back($1);
-      l->push_back($3);
-      $$ = new ExprConcatStrings(l);
-    }
-  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists($1, $3); }
+  : '!' expr_op %prec NEG { $$ = makeOpNot($2); }
+  | expr_op EQ expr_op { $$ = makeOpEq($1, $3); }
+  | expr_op NEQ expr_op { $$ = makeOpNEq($1, $3); }
+  | expr_op AND expr_op { $$ = makeOpAnd($1, $3); }
+  | expr_op OR expr_op { $$ = makeOpOr($1, $3); }
+  | expr_op IMPL expr_op { $$ = makeOpImpl($1, $3); }
+  | expr_op UPDATE expr_op { $$ = makeOpUpdate($1, $3); }
+  | expr_op '~' expr_op { $$ = makeSubPath($1, $3); }
+  | expr_op '?' ID { $$ = makeOpHasAttr($1, $3); }
+  | expr_op '+' expr_op { $$ = makeOpPlus($1, $3); }
+  | expr_op CONCAT expr_op { $$ = makeOpConcat($1, $3); }
  | expr_app
  ;

 expr_app
  : expr_app expr_select
-    { $$ = new ExprApp($1, $2); }
+    { $$ = makeCall($1, $2); }
  | expr_select { $$ = $1; }
  ;

 expr_select
  : expr_select '.' ID
-    { $$ = new ExprSelect($1, data->symbols.create($3)); }
+    { $$ = makeSelect($1, $3); }
  | expr_simple { $$ = $1; }
  ;

 expr_simple
-  : ID { $$ = new ExprVar(data->symbols.create($1)); }
-  | INT { $$ = new ExprInt($1); }
+  : ID { $$ = makeVar($1); }
+  | INT { $$ = makeInt(ATgetInt((ATermInt) $1)); }
  | '"' string_parts '"' {
      /* For efficiency, and to simplify parse trees a bit. */
-      if ($2->empty()) $$ = new ExprString("");
-      else if ($2->size() == 1) $$ = $2->front();
-      else $$ = new ExprConcatStrings($2);
+      if ($2 == ATempty) $$ = makeStr(toATerm(""), ATempty);
+      else if (ATgetNext($2) == ATempty) $$ = ATgetFirst($2);
+      else $$ = makeConcatStrings(ATreverse($2));
  }
  | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
-      $$ = stripIndentation(*$2);
+      $$ = stripIndentation(ATreverse($2));
  }
-  | PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
-  | URI { $$ = new ExprString($1); }
+  | PATH { $$ = makePath(toATerm(absPath(aterm2String($1), data->basePath))); }
+  | URI { $$ = makeStr($1, ATempty); }
  | '(' expr ')' { $$ = $2; }
  /* Let expressions `let {..., body = ...}' are just desugared
     into `(rec {..., body = ...}).body'. */
  | LET '{' binds '}'
-    { $3->recursive = true; $$ = new ExprSelect($3, data->symbols.create("body")); }
+    { $$ = makeSelect(fixAttrs(true, $3), toATerm("body")); }
  | REC '{' binds '}'
-    { $3->recursive = true; $$ = $3; }
+    { $$ = fixAttrs(true, $3); }
  | '{' binds '}'
-    { $$ = $2; }
-  | '[' expr_list ']' { $$ = $2; }
+    { $$ = fixAttrs(false, $2); }
+  | '[' expr_list ']' { $$ = makeList(ATreverse($2)); }
  ;

 string_parts
-  : string_parts STR { $$ = $1; $1->push_back($2); }
-  | string_parts DOLLAR_CURLY expr '}' { backToString(scanner); $$ = $1; $1->push_back($3); }
-  | { $$ = new vector<Expr *>; }
+  : string_parts STR { $$ = ATinsert($1, $2); }
+  | string_parts DOLLAR_CURLY expr '}' { backToString(scanner); $$ = ATinsert($1, $3); }
+  | { $$ = ATempty; }
  ;

 ind_string_parts
-  : ind_string_parts IND_STR { $$ = $1; $1->push_back($2); }
-  | ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = $1; $1->push_back($3); }
-  | { $$ = new vector<Expr *>; }
+  : ind_string_parts IND_STR { $$ = ATinsert($1, $2); }
+  | ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = ATinsert($1, $3); }
+  | { $$ = ATempty; }
+  ;
+
+pattern
+  : pattern2 '@' pattern { $$ = makeAtPat($1, $3); }
+  | pattern2
+  ;
+
+pattern2
+  : ID { $$ = makeVarPat($1); }
+  | '{' formals '}' { $$ = makeAttrsPat($2.formals, $2.ellipsis ? eTrue : eFalse); }
  ;

 binds
-  : binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
-  | binds INHERIT ids ';'
-    { $$ = $1;
-      foreach (vector<Symbol>::iterator, i, *$3) {
-          if ($$->attrNames.find(*i) != $$->attrNames.end())
-              dupAttr(*i, makeCurPos(@3, data), $$->attrNames[*i]);
-          Pos pos = makeCurPos(@3, data);
-          $$->inherited.push_back(ExprAttrs::Inherited(*i, pos));
-          $$->attrNames[*i] = pos;
-      }
-    }
-  | binds INHERIT '(' expr ')' ids ';'
-    { $$ = $1;
-      /* !!! Should ensure sharing of the expression in $4. */
-      foreach (vector<Symbol>::iterator, i, *$6) {
-          if ($$->attrNames.find(*i) != $$->attrNames.end())
-              dupAttr(*i, makeCurPos(@6, data), $$->attrNames[*i]);
-          $$->attrs[*i] = ExprAttrs::Attr(new ExprSelect($4, *i), makeCurPos(@6, data));
-          $$->attrNames[*i] = makeCurPos(@6, data);
-      }}
-
-  | { $$ = new ExprAttrs; }
+  : binds bind { $$ = ATinsert($1, $2); }
+  | { $$ = ATempty; }
  ;

-ids
-  : ids ID { $$ = $1; $1->push_back(data->symbols.create($2)); /* !!! dangerous */ }
-  | { $$ = new vector<Symbol>; }
+bind
+  : attrpath '=' expr ';'
+    { $$ = makeBindAttrPath(ATreverse($1), $3, CUR_POS); }
+  | INHERIT inheritsrc ids ';'
+    { $$ = makeInherit($2, $3, CUR_POS); }
  ;

+inheritsrc
+  : '(' expr ')' { $$ = $2; }
+  | { $$ = makeScope(); }
+  ;
+
+ids: ids ID { $$ = ATinsert($1, $2); } | { $$ = ATempty; };
+
 attrpath
-  : attrpath '.' ID { $$ = $1; $1->push_back(data->symbols.create($3)); }
-  | ID { $$ = new vector<Symbol>; $$->push_back(data->symbols.create($1)); }
+  : attrpath '.' ID { $$ = ATinsert($1, $3); }
+  | ID { $$ = ATmakeList1($1); }
  ;

 expr_list
-  : expr_list expr_select { $$ = $1; $1->elems.push_back($2); /* !!! dangerous */ }
-  | { $$ = new ExprList; }
+  : expr_list expr_select { $$ = ATinsert($1, $2); }
+  | { $$ = ATempty; }
  ;

 formals
-  : formal ',' formals
-    { $$ = $3; addFormal(CUR_POS, $$, *$1); }
+  : formal ',' formals /* !!! right recursive */
+    { $$.formals = ATinsert($3.formals, $1); $$.ellipsis = $3.ellipsis; }
  | formal
-    { $$ = new Formals; addFormal(CUR_POS, $$, *$1); $$->ellipsis = false; }
+    { $$.formals = ATinsert(ATempty, $1); $$.ellipsis = false; }
  |
-    { $$ = new Formals; $$->ellipsis = false; }
+    { $$.formals = ATempty; $$.ellipsis = false; }
  | ELLIPSIS
-    { $$ = new Formals; $$->ellipsis = true; }
+    { $$.formals = ATempty; $$.ellipsis = true; }
  ;

 formal
-  : ID { $$ = new Formal(data->symbols.create($1), 0); }
-  | ID '?' expr { $$ = new Formal(data->symbols.create($1), $3); }
+  : ID { $$ = makeFormal($1, makeNoDefaultValue()); }
+  | ID '?' expr { $$ = makeFormal($1, makeDefaultValue($3)); }
  ;
  
 %%


+#include "eval.hh"  
+
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>

-#include <eval.hh>
-

 namespace nix {
      

-static Expr * parse(EvalState & state, const char * text,
-    const Path & path, const Path & basePath)
+static Expr parse(EvalState & state,
+    const char * text, const Path & path,
+    const Path & basePath)
 {
    yyscan_t scanner;
-    ParseData data(state.symbols);
+    ParseData data;
    data.basePath = basePath;
    data.path = path;

@@ -456,7 +512,7 @@ static Expr * parse(EvalState & state, const char * text,
    if (res) throw ParseError(data.error);

    try {
-        data.result->bindVars(state.staticBaseEnv);
+        checkVarDefs(state.primOps, data.result);
    } catch (Error & e) {
        throw ParseError(format("%1%, in `%2%'") % e.msg() % path);
    }
@@ -465,10 +521,16 @@ static Expr * parse(EvalState & state, const char * text,
 }


-Expr * parseExprFromFile(EvalState & state, Path path)
+Expr parseExprFromFile(EvalState & state, Path path)
 {
    assert(path[0] == '/');

+#if 0
+    /* Perhaps this is already an imploded parse tree? */
+    Expr e = ATreadFromNamedFile(path.c_str());
+    if (e) return e;
+#endif
+
    /* If `path' is a symlink, follow it.  This is so that relative
       path references work. */
    struct stat st;
@@ -490,7 +552,7 @@ Expr * parseExprFromFile(EvalState & state, Path path)
 }


-Expr * parseExprFromString(EvalState & state,
+Expr parseExprFromString(EvalState & state,
    const string & s, const Path & basePath)
 {
    return parse(state, s.c_str(), "(string)", basePath);
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
--- a/src/libexpr/symbol-table.hh
+++ b/src/libexpr/symbol-table.hh
@@ -1,81 +0,0 @@
-#ifndef __SYMBOL_TABLE_H
-#define __SYMBOL_TABLE_H
-
-#include <map>
-#include <tr1/unordered_set>
-
-#include "types.hh"
-
-namespace nix {
-
-/* Symbol table used by the parser and evaluator to represent and look
-   up identifiers and attribute sets efficiently.
-   SymbolTable::create() converts a string into a symbol.  Symbols
-   have the property that they can be compared efficiently (using a
-   pointer equality test), because the symbol table stores only one
-   copy of each string. */
-
-class Symbol
-{
-private:
-    const string * s; // pointer into SymbolTable
-    Symbol(const string * s) : s(s) { };
-    friend class SymbolTable;
-
-public:
-    bool operator == (const Symbol & s2) const
-    {
-        return s == s2.s;
-    }
-    
-    bool operator != (const Symbol & s2) const
-    {
-        return s != s2.s;
-    }
-    
-    bool operator < (const Symbol & s2) const
-    {
-        return s < s2.s;
-    }
-
-    operator const string & () const
-    {
-        return *s;
-    }
-
-    bool empty() const
-    {
-        return s->empty();
-    }
-
-    friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
-};
-
-inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
-{
-    str << *sym.s;
-    return str;
-}
-
-class SymbolTable
-{
-private:
-    typedef std::tr1::unordered_set<string> Symbols;
-    Symbols symbols;
-
-public:
-    Symbol create(const string & s)
-    {
-        std::pair<Symbols::iterator, bool> res = symbols.insert(s);
-        return Symbol(&*res.first);
-    }
-
-    unsigned int size() const
-    {
-        return symbols.size();
-    }
-};
-
-}
-
-#endif /* !__SYMBOL_TABLE_H */
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -1,161 +0,0 @@
-#include "value-to-xml.hh"
-#include "xml-writer.hh"
-#include "util.hh"
-
-#include <cstdlib>
-
-
-namespace nix {
-
-    
-static XMLAttrs singletonAttrs(const string & name, const string & value)
-{
-    XMLAttrs attrs;
-    attrs[name] = value;
-    return attrs;
-}
-
-
-static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen);
-
-
-static void posToXML(XMLAttrs & xmlAttrs, const Pos & pos)
-{
-    xmlAttrs["path"] = pos.file;
-    xmlAttrs["line"] = (format("%1%") % pos.line).str();
-    xmlAttrs["column"] = (format("%1%") % pos.column).str();
-}
-
-
-static void showAttrs(EvalState & state, bool strict, bool location,
-    Bindings & attrs, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
-{
-    StringSet names;
-    
-    foreach (Bindings::iterator, i, attrs)
-        names.insert(i->first);
-    
-    foreach (StringSet::iterator, i, names) {
-        Attr & a(attrs[state.symbols.create(*i)]);
-        
-        XMLAttrs xmlAttrs;
-        xmlAttrs["name"] = *i;
-        if (location && a.pos != &noPos) posToXML(xmlAttrs, *a.pos);
-        
-        XMLOpenElement _(doc, "attr", xmlAttrs);
-        printValueAsXML(state, strict, location,
-            a.value, doc, context, drvsSeen);
-    }
-}
-
-
-static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
-{
-    checkInterrupt();
-
-    if (strict) state.forceValue(v);
-        
-    switch (v.type) {
-
-        case tInt:
-            doc.writeEmptyElement("int", singletonAttrs("value", (format("%1%") % v.integer).str()));
-            break;
-
-        case tBool:
-            doc.writeEmptyElement("bool", singletonAttrs("value", v.boolean ? "true" : "false"));
-            break;
-
-        case tString:
-            /* !!! show the context? */
-            doc.writeEmptyElement("string", singletonAttrs("value", v.string.s));
-            break;
-
-        case tPath:
-            doc.writeEmptyElement("path", singletonAttrs("value", v.path));
-            break;
-
-        case tNull:
-            doc.writeEmptyElement("null");
-            break;
-
-        case tAttrs:
-            if (state.isDerivation(v)) {
-                XMLAttrs xmlAttrs;
-            
-                Bindings::iterator a = v.attrs->find(state.symbols.create("derivation"));
-
-                Path drvPath;
-                a = v.attrs->find(state.sDrvPath);
-                if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(a->second.value);
-                    if (a->second.value.type == tString)
-                        xmlAttrs["drvPath"] = drvPath = a->second.value.string.s;
-                }
-        
-                a = v.attrs->find(state.sOutPath);
-                if (a != v.attrs->end()) {
-                    if (strict) state.forceValue(a->second.value);
-                    if (a->second.value.type == tString)
-                        xmlAttrs["outPath"] = a->second.value.string.s;
-                }
-
-                XMLOpenElement _(doc, "derivation", xmlAttrs);
-
-                if (drvPath != "" && drvsSeen.find(drvPath) == drvsSeen.end()) {
-                    drvsSeen.insert(drvPath);
-                    showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
-                } else
-                    doc.writeEmptyElement("repeated");
-            }
-
-            else {
-                XMLOpenElement _(doc, "attrs");
-                showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
-            }
-            
-            break;
-
-        case tList: {
-            XMLOpenElement _(doc, "list");
-            for (unsigned int n = 0; n < v.list.length; ++n)
-                printValueAsXML(state, strict, location, *v.list.elems[n], doc, context, drvsSeen);
-            break;
-        }
-
-        case tLambda: {
-            XMLAttrs xmlAttrs;
-            if (location) posToXML(xmlAttrs, v.lambda.fun->pos);
-            XMLOpenElement _(doc, "function", xmlAttrs);
-            
-            if (v.lambda.fun->matchAttrs) {
-                XMLAttrs attrs;
-                if (!v.lambda.fun->arg.empty()) attrs["name"] = v.lambda.fun->arg;
-                if (v.lambda.fun->formals->ellipsis) attrs["ellipsis"] = "1";
-                XMLOpenElement _(doc, "attrspat", attrs);
-                foreach (Formals::Formals_::iterator, i, v.lambda.fun->formals->formals)
-                    doc.writeEmptyElement("attr", singletonAttrs("name", i->name));
-            } else
-                doc.writeEmptyElement("varpat", singletonAttrs("name", v.lambda.fun->arg));
-            
-            break;
-        }
-
-        default:
-            doc.writeEmptyElement("unevaluated");
-    }
-}
-
-
-void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context)
-{
-    XMLWriter doc(true, out);
-    XMLOpenElement root(doc, "expr");
-    PathSet drvsSeen;    
-    printValueAsXML(state, strict, location, v, doc, context, drvsSeen);
-}
-
- 
-}
--- a/src/libexpr/value-to-xml.hh
+++ b/src/libexpr/value-to-xml.hh
@@ -1,17 +0,0 @@
-#ifndef __VALUE_TO_XML_H
-#define __VALUE_TO_XML_H
-
-#include <string>
-#include <map>
-
-#include "nixexpr.hh"
-#include "eval.hh"
-
-namespace nix {
-
-void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context);
-    
-}
-
-#endif /* !__VALUE_TO_XML_H */
--- a/src/libmain/Makefile.am
+++ b/src/libmain/Makefile.am
@@ -15,5 +15,5 @@ AM_CXXFLAGS = \
 -DNIX_LIBEXEC_DIR=\"$(libexecdir)\" \
 -DNIX_BIN_DIR=\"$(bindir)\" \
 -DNIX_VERSION=\"$(VERSION)\" \
- -I$(srcdir)/.. -I$(srcdir)/../libutil \
+ -I$(srcdir)/.. ${aterm_include} -I$(srcdir)/../libutil \
 -I$(srcdir)/../libstore
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -13,6 +13,8 @@
 #include <sys/stat.h>
 #include <unistd.h>

+#include <aterm2.h>
+

 namespace nix {

@@ -85,6 +87,21 @@ static void setLogType(string lt)
 }


+unsigned long long getIntArg(const string & opt,
+    Strings::iterator & i, const Strings::iterator & end)
+{
+    ++i;
+    if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
+    long long n;
+    if (!string2Int(*i, n) || n < 0)
+        throw UsageError(format("`%1%' requires a non-negative integer") % opt);
+    return n;
+}
+
+
+void initDerivationsHelpers();
+
+
 static void closeStore()
 {
    try {
@@ -138,29 +155,23 @@ static void initAndRun(int argc, char * * argv)
    maxSilentTime = queryIntSetting("build-max-silent-time", 0);

    /* Catch SIGINT. */
-    struct sigaction act;
+    struct sigaction act, oact;
    act.sa_handler = sigintHandler;
    sigfillset(&act.sa_mask);
    act.sa_flags = 0;
-    if (sigaction(SIGINT, &act, 0))
+    if (sigaction(SIGINT, &act, &oact))
        throw SysError("installing handler for SIGINT");
-    if (sigaction(SIGTERM, &act, 0))
+    if (sigaction(SIGTERM, &act, &oact))
        throw SysError("installing handler for SIGTERM");
-    if (sigaction(SIGHUP, &act, 0))
+    if (sigaction(SIGHUP, &act, &oact))
        throw SysError("installing handler for SIGHUP");

    /* Ignore SIGPIPE. */
    act.sa_handler = SIG_IGN;
    act.sa_flags = 0;
-    if (sigaction(SIGPIPE, &act, 0))
+    if (sigaction(SIGPIPE, &act, &oact))
        throw SysError("ignoring SIGPIPE");

-    /* Reset SIGCHLD to its default. */
-    act.sa_handler = SIG_DFL;
-    act.sa_flags = 0;
-    if (sigaction(SIGCHLD, &act, 0))
-        throw SysError("resetting SIGCHLD");
-
    /* There is no privacy in the Nix system ;-)  At least not for
       now.  In particular, store objects should be readable by
       everybody.  This prevents nasty surprises when using a shared
@@ -171,6 +182,9 @@ static void initAndRun(int argc, char * * argv)
    string lt = getEnv("NIX_LOG_TYPE");
    if (lt != "") setLogType(lt);

+    /* ATerm stuff.  !!! find a better place to put this */
+    initDerivationsHelpers();
+    
    /* Put the arguments in a vector. */
    Strings args, remaining;
    while (argc--) args.push_back(*argv++);
@@ -181,7 +195,7 @@ static void initAndRun(int argc, char * * argv)
    for (Strings::iterator i = args.begin(); i != args.end(); ++i) {
        string arg = *i;
        if (string(arg, 0, 4) == "-at-") ;
-        else if (arg.length() > 2 && arg[0] == '-' && arg[1] != '-' && !isdigit(arg[1])) {
+        else if (arg.length() > 2 && arg[0] == '-' && arg[1] != '-') {
            for (unsigned int j = 1; j < arg.length(); j++)
                if (isalpha(arg[j]))
                    remaining.push_back((string) "-" + arg[j]);
@@ -225,11 +239,11 @@ static void initAndRun(int argc, char * * argv)
        else if (arg == "--fallback")
            tryFallback = true;
        else if (arg == "--max-jobs" || arg == "-j")
-            maxBuildJobs = getIntArg<unsigned int>(arg, i, args.end());
+            maxBuildJobs = getIntArg(arg, i, args.end());
        else if (arg == "--readonly-mode")
            readOnlyMode = true;
        else if (arg == "--max-silent-time")
-            maxSilentTime = getIntArg<unsigned int>(arg, i, args.end());
+            maxSilentTime = getIntArg(arg, i, args.end());
        else if (arg == "--no-build-hook")
            useBuildHook = false;
        else if (arg == "--show-trace")
@@ -325,6 +339,10 @@ int main(int argc, char * * argv)
    if (argc == 0) abort();
    setuidInit();
    
+    /* ATerm setup. */
+    ATerm bottomOfStack;
+    ATinit(argc, argv, &bottomOfStack);
+
    /* Turn on buffering for cerr. */
 #if HAVE_PUBSETBUF
    std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -22,30 +22,22 @@ extern std::string programId;

 namespace nix {

-MakeError(UsageError, nix::Error);
-
 /* Ugh.  No better place to put this. */
 Path makeRootName(const Path & gcRoot, int & counter);
 void printGCWarning();

 void printMissing(const PathSet & paths);

-template<class N> N getIntArg(const string & opt,
-    Strings::iterator & i, const Strings::iterator & end)
-{
-    ++i;
-    if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
-    N n;
-    if (!string2Int(*i, n))
-        throw UsageError(format("`%1%' requires an integer argument") % opt);
-    return n;
-}
+unsigned long long getIntArg(const string & opt,
+    Strings::iterator & i, const Strings::iterator & end);

 /* Whether we're running setuid. */
 extern bool setuidMode;

 extern volatile ::sig_atomic_t blockInt;

+MakeError(UsageError, nix::Error);
+
 struct RemoveTempRoots 
 {
    ~RemoveTempRoots();    
--- a/src/libstore/Makefile.am
+++ b/src/libstore/Makefile.am
@@ -2,15 +2,22 @@ pkglib_LTLIBRARIES = libstore.la

 libstore_la_SOURCES = \
  store-api.cc local-store.cc remote-store.cc derivations.cc build.cc misc.cc \
-  globals.cc references.cc pathlocks.cc gc.cc \
+  globals.cc db.cc references.cc pathlocks.cc gc.cc upgrade-schema.cc \
  optimise-store.cc

 pkginclude_HEADERS = \
  store-api.hh local-store.hh remote-store.hh derivations.hh misc.hh \
-  globals.hh references.hh pathlocks.hh \
+  globals.hh db.hh references.hh pathlocks.hh \
  worker-protocol.hh

-libstore_la_LIBADD = ../libutil/libutil.la ../boost/format/libformat.la @ADDITIONAL_NETWORK_LIBS@
+libstore_la_LIBADD = ../libutil/libutil.la ../boost/format/libformat.la
+
+BUILT_SOURCES = derivations-ast.cc derivations-ast.hh
+
+EXTRA_DIST = derivations-ast.def derivations-ast.cc

 AM_CXXFLAGS = -Wall \
- -I$(srcdir)/.. -I$(srcdir)/../libutil
+ -I$(srcdir)/.. ${bdb_include} ${aterm_include} -I$(srcdir)/../libutil
+
+derivations-ast.cc derivations-ast.hh: ../aterm-helper.pl derivations-ast.def
+	$(perl) $(srcdir)/../aterm-helper.pl derivations-ast.hh derivations-ast.cc < $(srcdir)/derivations-ast.def
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1,12 +1,9 @@
-#include "config.h"
-
 #include "references.hh"
 #include "pathlocks.hh"
 #include "misc.hh"
 #include "globals.hh"
 #include "local-store.hh"
 #include "util.hh"
-#include "archive.hh"

 #include <map>
 #include <iostream>
@@ -18,19 +15,19 @@

 #include <time.h>
 #include <sys/time.h>
-#include <sys/wait.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
-#include <stdio.h>

 #include <pwd.h>
 #include <grp.h>


 /* Includes required for chroot support. */
+#include "config.h"
+
 #if HAVE_SYS_PARAM_H
 #include <sys/param.h>
 #endif
@@ -162,7 +159,6 @@ struct Child
 {
    WeakGoalPtr goal;
    set<int> fds;
-    bool monitorForSilence;
    bool inBuildSlot;
    time_t lastOutput; /* time we last got output on stdout/stderr */
 };
@@ -235,7 +231,7 @@ public:
    /* Registers a running child process.  `inBuildSlot' means that
       the process counts towards the jobs limit. */
    void childStarted(GoalPtr goal, pid_t pid,
-        const set<int> & fds, bool inBuildSlot, bool monitorForSilence);
+        const set<int> & fds, bool inBuildSlot);

    /* Unregisters a running child process.  `wakeSleepers' should be
       false if there is no sense in waking up goals that are sleeping
@@ -470,8 +466,6 @@ void UserLock::acquire()
        if (!pw)
            throw Error(format("the user `%1%' in the group `%2%' does not exist")
                % *i % buildUsersGroup);
-
-        createDirs(nixStateDir + "/userpool");
        
        fnUserLock = (format("%1%/userpool/%2%") % nixStateDir % pw->pw_uid).str();

@@ -797,9 +791,6 @@ void DerivationGoal::init()
 {
    trace("init");

-    if (readOnlyMode)
-        throw Error(format("cannot build derivation `%1%' - no write access to the Nix store") % drvPath);
-
    /* The first thing to do is to make sure that the derivation
       exists.  If it doesn't, it may be created through a
       substitute. */
@@ -1263,7 +1254,7 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
    pid.setKillSignal(SIGTERM);
    logPipe.writeSide.close();
    worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), false, false);
+        pid, singleton<set<int> >(logPipe.readSide), false);

    toHook.readSide.close();

@@ -1319,18 +1310,18 @@ DerivationGoal::HookReply DerivationGoal::tryBuildHook()
        string s;
        foreach (PathSet::iterator, i, allInputs) s += *i + "\n";
        
-        writeFile(inputListFN, s);
+        writeStringToFile(inputListFN, s);

        /* The `outputs' file lists all outputs that have to be copied
           from the remote system. */
        s = "";
        foreach (DerivationOutputs::iterator, i, drv.outputs)
            s += i->second.path + "\n";
-        writeFile(outputListFN, s);
+        writeStringToFile(outputListFN, s);

        /* The `references' file has exactly the format accepted by
           `nix-store --register-validity'. */
-        writeFile(referencesFN,
+        writeStringToFile(referencesFN,
            makeValidityRegistration(allInputs, true, false));

        /* Tell the hook to proceed. */
@@ -1494,7 +1485,7 @@ void DerivationGoal::startBuilder()
        }

        /* Write closure info to `fileName'. */
-        writeFile(tmpDir + "/" + fileName,
+        writeStringToFile(tmpDir + "/" + fileName,
            makeValidityRegistration(paths, false, false));
    }

@@ -1566,23 +1557,16 @@ void DerivationGoal::startBuilder()
        createDirs(chrootTmpDir);
        chmod(chrootTmpDir, 01777);

-        /* Create a /etc/passwd with entries for the build user and the
-           nobody account.  The latter is kind of a hack to support
-           Samba-in-QEMU.  */
+        /* Create a /etc/passwd with entries for the build user and
+           the nobody account.  The latter is kind of a hack to
+           support Samba-in-QEMU. */
        createDirs(chrootRootDir + "/etc");

-        writeFile(chrootRootDir + "/etc/passwd",
+        writeStringToFile(chrootRootDir + "/etc/passwd",
            (format(
-                "nixbld:x:%1%:%2%:Nix build user:/:/noshell\n"
+                "nixbld:x:%1%:65534:Nix build user:/:/noshell\n"
                "nobody:x:65534:65534:Nobody:/:/noshell\n")
-                % (buildUser.enabled() ? buildUser.getUID() : getuid())
-	        % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
-
-	/* Declare the build user's group so that programs get a consistent
-	   view of the system (e.g., "id -gn").  */
-	writeFile(chrootRootDir + "/etc/group",
-		  (format("nixbld:!:%1%:\n")
-		   % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
+                % (buildUser.enabled() ? buildUser.getUID() : getuid())).str());

        /* Bind-mount a user-configurable set of directories from the
           host file system.  The `/dev/pts' directory must be mounted
@@ -1616,18 +1600,8 @@ void DerivationGoal::startBuilder()
                dirsInChroot.insert(*i);
            else {
                Path p = chrootRootDir + *i;
-                if (link(i->c_str(), p.c_str()) == -1) {
-                    /* Hard-linking fails if we exceed the maximum
-                       link count on a file (e.g. 32000 of ext3),
-                       which is quite possible after a `nix-store
-                       --optimise'.  Make a copy instead. */
-                    if (errno != EMLINK)
-                        throw SysError(format("linking `%1%' to `%2%'") % p % *i);
-                    StringSink sink;
-                    dumpPath(*i, sink);
-                    StringSource source(sink.s);
-                    restorePath(p, source);
-                }
+                if (link(i->c_str(), p.c_str()) == -1)
+                    throw SysError(format("linking `%1%' to `%2%'") % p % *i);
            }
        }
        
@@ -1775,7 +1749,7 @@ void DerivationGoal::startBuilder()
    pid.setSeparatePG(true);
    logPipe.writeSide.close();
    worker.childStarted(shared_from_this(), pid,
-        singleton<set<int> >(logPipe.readSide), true, true);
+        singleton<set<int> >(logPipe.readSide), true);

    if (printBuildTrace) {
        printMsg(lvlError, format("@ build-started %1% %2% %3% %4%")
@@ -2133,9 +2107,6 @@ void SubstitutionGoal::init()
        return;
    }

-    if (readOnlyMode)
-        throw Error(format("cannot substitute path `%1%' - no write access to the Nix store") % storePath);
-
    subs = substituters;
    
    tryNext();
@@ -2282,7 +2253,7 @@ void SubstitutionGoal::tryToRun()
    pid.setKillSignal(SIGTERM);
    logPipe.writeSide.close();
    worker.childStarted(shared_from_this(),
-        pid, singleton<set<int> >(logPipe.readSide), true, true);
+        pid, singleton<set<int> >(logPipe.readSide), true);

    state = &SubstitutionGoal::finished;

@@ -2482,15 +2453,13 @@ unsigned Worker::getNrLocalBuilds()


 void Worker::childStarted(GoalPtr goal,
-    pid_t pid, const set<int> & fds, bool inBuildSlot,
-    bool monitorForSilence)
+    pid_t pid, const set<int> & fds, bool inBuildSlot)
 {
    Child child;
    child.goal = goal;
    child.fds = fds;
    child.lastOutput = time(0);
    child.inBuildSlot = inBuildSlot;
-    child.monitorForSilence = monitorForSilence;
    children[pid] = child;
    if (inBuildSlot) nrLocalBuilds++;
 }
@@ -2611,16 +2580,12 @@ void Worker::waitForInput()
    if (maxSilentTime != 0) {
        time_t oldest = 0;
        foreach (Children::iterator, i, children) {
-            if (i->second.monitorForSilence) {
-                oldest = oldest == 0 || i->second.lastOutput < oldest
-                    ? i->second.lastOutput : oldest;
-            }
-        }
-        if (oldest) {
-            useTimeout = true;
-            timeout.tv_sec = std::max((time_t) 0, oldest + maxSilentTime - before);
-            printMsg(lvlVomit, format("sleeping %1% seconds") % timeout.tv_sec);
+            oldest = oldest == 0 || i->second.lastOutput < oldest
+                ? i->second.lastOutput : oldest;
        }
+        useTimeout = true;
+        timeout.tv_sec = std::max((time_t) 0, oldest + maxSilentTime - before);
+        printMsg(lvlVomit, format("sleeping %1% seconds") % timeout.tv_sec);
    }

    /* If we are polling goals that are waiting for a lock, then wake
@@ -2695,7 +2660,6 @@ void Worker::waitForInput()
        }

        if (maxSilentTime != 0 &&
-            j->second.monitorForSilence &&
            after - j->second.lastOutput >= (time_t) maxSilentTime)
        {
            printMsg(lvlError,
--- a/src/libstore/db.cc
+++ b/src/libstore/db.cc
@@ -0,0 +1,474 @@
+#include "config.h"
+
+#ifdef OLD_DB_COMPAT
+
+#include "db.hh"
+#include "util.hh"
+#include "pathlocks.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include <memory>
+
+#include <db_cxx.h>
+
+
+namespace nix {
+
+
+/* Wrapper class to ensure proper destruction. */
+class DestroyDbc 
+{
+    Dbc * dbc;
+public:
+    DestroyDbc(Dbc * _dbc) : dbc(_dbc) { }
+    ~DestroyDbc() { dbc->close(); /* close() frees dbc */ }
+};
+
+
+class DestroyDbEnv
+{
+    DbEnv * dbenv;
+public:
+    DestroyDbEnv(DbEnv * _dbenv) : dbenv(_dbenv) { }
+    ~DestroyDbEnv() {
+        if (dbenv) {
+            if (dbenv->get_DB_ENV()) dbenv->close(0);
+            delete dbenv;
+        }
+    }
+    void release() { dbenv = 0; };
+};
+
+
+static void rethrow(DbException & e)
+{
+    throw Error(e.what());
+}
+
+
+Transaction::Transaction()
+    : txn(0)
+{
+}
+
+
+Transaction::Transaction(Database & db)
+    : txn(0)
+{
+    begin(db);
+}
+
+
+Transaction::~Transaction()
+{
+    if (txn) abort();
+}
+
+
+void Transaction::begin(Database & db)
+{
+    assert(txn == 0);
+    db.requireEnv();
+    try {
+        db.env->txn_begin(0, &txn, 0);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Transaction::commit()
+{
+    if (!txn) throw Error("commit called on null transaction");
+    debug(format("committing transaction %1%") % (void *) txn);
+    DbTxn * txn2 = txn;
+    txn = 0;
+    try {
+        txn2->commit(0);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Transaction::abort()
+{
+    if (!txn) throw Error("abort called on null transaction");
+    debug(format("aborting transaction %1%") % (void *) txn);
+    DbTxn * txn2 = txn;
+    txn = 0;
+    try {
+        txn2->abort();
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Transaction::moveTo(Transaction & t)
+{
+    if (t.txn) throw Error("target txn already exists");
+    t.txn = txn;
+    txn = 0;
+}
+
+
+void Database::requireEnv()
+{
+    checkInterrupt();
+    if (!env) throw Error("database environment is not open "
+        "(maybe you don't have sufficient permission?)");
+}
+
+
+Db * Database::getDb(TableId table)
+{
+    if (table == 0)
+        throw Error("database table is not open "
+            "(maybe you don't have sufficient permission?)");
+    std::map<TableId, Db *>::iterator i = tables.find(table);
+    if (i == tables.end())
+        throw Error("unknown table id");
+    return i->second;
+}
+
+
+Database::Database()
+    : env(0)
+    , nextId(1)
+{
+}
+
+
+Database::~Database()
+{
+    close();
+}
+
+
+void openEnv(DbEnv * & env, const string & path, u_int32_t flags)
+{
+    try {
+        createDirs(path);
+    } catch (SysError & e) {
+        if (e.errNo == EPERM || e.errNo == EACCES)
+            throw DbNoPermission(format("cannot create the Nix database in `%1%'") % path);
+        else
+            throw;
+    }
+        
+    try {
+        env->open(path.c_str(),
+            DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN |
+            DB_CREATE | flags,
+            0666);
+    } catch (DbException & e) {
+        printMsg(lvlError, format("environment open failed: %1%") % e.what());
+        throw;
+    }
+}
+
+
+static int my_fsync(int fd)
+{
+    return 0;
+}
+
+
+static void errorPrinter(const DbEnv * env, const char * errpfx, const char * msg)
+{
+    printMsg(lvlError, format("Berkeley DB error: %1%") % msg);
+}
+
+
+static void messagePrinter(const DbEnv * env, const char * msg)
+{
+    printMsg(lvlError, format("Berkeley DB message: %1%") % msg);
+}
+
+
+void Database::open2(const string & path, bool removeOldEnv)
+{
+    if (env) throw Error(format("environment already open"));
+
+    debug(format("opening database environment"));
+
+
+    /* Create the database environment object. */
+    DbEnv * env = new DbEnv(0);
+    DestroyDbEnv deleteEnv(env);
+
+    env->set_errcall(errorPrinter);
+    env->set_msgcall(messagePrinter);
+    if (getEnv("NIX_DEBUG_DB_REGISTER") == "1")
+        env->set_verbose(DB_VERB_REGISTER, 1);
+    env->set_verbose(DB_VERB_RECOVERY, 1);
+    
+    /* Smaller log files. */
+    env->set_lg_bsize(32 * 1024); /* default */
+    env->set_lg_max(256 * 1024); /* must be > 4 * lg_bsize */
+    
+    /* Write the log, but don't sync.  This protects transactions
+       against application crashes, but if the system crashes, some
+       transactions may be undone.  An acceptable risk, I think. */
+    env->set_flags(DB_TXN_WRITE_NOSYNC | DB_LOG_AUTOREMOVE, 1);
+    
+    /* Increase the locking limits.  If you ever get `Dbc::get: Cannot
+       allocate memory' or similar, especially while running
+       `nix-store --verify', just increase the following number, then
+       run db_recover on the database to remove the existing DB
+       environment (since changes only take effect on new
+       environments). */
+    env->set_lk_max_locks(10000);
+    env->set_lk_max_lockers(10000);
+    env->set_lk_max_objects(10000);
+    env->set_lk_detect(DB_LOCK_DEFAULT);
+    
+    /* Dangerous, probably, but from the docs it *seems* that BDB
+       shouldn't sync when DB_TXN_WRITE_NOSYNC is used, but it still
+       fsync()s sometimes. */
+    db_env_set_func_fsync(my_fsync);
+
+    
+    if (removeOldEnv) {
+        printMsg(lvlError, "removing old Berkeley DB database environment...");
+        env->remove(path.c_str(), DB_FORCE);
+        return;
+    }
+
+    openEnv(env, path, DB_REGISTER | DB_RECOVER);
+
+    deleteEnv.release();
+    this->env = env;
+}
+
+
+void Database::open(const string & path)
+{
+    try {
+
+        open2(path, false);
+        
+    } catch (DbException e) {
+        
+        if (e.get_errno() == DB_VERSION_MISMATCH) {
+            /* Remove the environment while we are holding the global
+               lock.  If things go wrong there, we bail out.
+               !!! argh, we abolished the global lock :-( */
+            open2(path, true);
+
+            /* Try again. */
+            open2(path, false);
+
+            /* Force a checkpoint, as per the BDB docs. */
+            env->txn_checkpoint(DB_FORCE, 0, 0);
+
+            printMsg(lvlError, "database succesfully upgraded to new version");
+        }
+
+#if 0        
+        else if (e.get_errno() == DB_RUNRECOVERY) {
+            /* If recovery is needed, do it. */
+            printMsg(lvlError, "running recovery...");
+            open2(path, false, true);
+        }
+#endif        
+        
+        else
+            rethrow(e);
+    }
+}
+
+
+void Database::close()
+{
+    if (!env) return;
+
+    /* Close the database environment. */
+    debug(format("closing database environment"));
+
+    try {
+
+        for (std::map<TableId, Db *>::iterator i = tables.begin();
+             i != tables.end(); )
+        {
+            std::map<TableId, Db *>::iterator j = i;
+            ++j;
+            closeTable(i->first);
+            i = j;
+        }
+
+        /* Do a checkpoint every 128 kilobytes, or every 5 minutes. */
+        env->txn_checkpoint(128, 5, 0);
+        
+        env->close(0);
+
+    } catch (DbException e) { rethrow(e); }
+
+    delete env;
+
+    env = 0;
+}
+
+
+TableId Database::openTable(const string & tableName, bool sorted)
+{
+    requireEnv();
+    TableId table = nextId++;
+
+    try {
+
+        Db * db = new Db(env, 0);
+
+        try {
+            db->open(0, tableName.c_str(), 0, 
+                sorted ? DB_BTREE : DB_HASH,
+                DB_CREATE | DB_AUTO_COMMIT, 0666);
+        } catch (...) {
+            delete db;
+            throw;
+        }
+
+        tables[table] = db;
+
+    } catch (DbException e) { rethrow(e); }
+
+    return table;
+}
+
+
+void Database::closeTable(TableId table)
+{
+    try {
+        Db * db = getDb(table);
+        db->close(DB_NOSYNC);
+        delete db;
+        tables.erase(table);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Database::deleteTable(const string & table)
+{
+    try {
+        env->dbremove(0, table.c_str(), 0, DB_AUTO_COMMIT);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+bool Database::queryString(const Transaction & txn, TableId table, 
+    const string & key, string & data)
+{
+    checkInterrupt();
+
+    try {
+        Db * db = getDb(table);
+
+        Dbt kt((void *) key.c_str(), key.length());
+        Dbt dt;
+
+        int err = db->get(txn.txn, &kt, &dt, 0);
+        if (err) return false;
+
+        if (!dt.get_data())
+            data = "";
+        else
+            data = string((char *) dt.get_data(), dt.get_size());
+    
+    } catch (DbException e) { rethrow(e); }
+
+    return true;
+}
+
+
+bool Database::queryStrings(const Transaction & txn, TableId table, 
+    const string & key, Strings & data)
+{
+    string d;
+    if (!queryString(txn, table, key, d))
+        return false;
+    data = unpackStrings(d);
+    return true;
+}
+
+
+void Database::setString(const Transaction & txn, TableId table,
+    const string & key, const string & data)
+{
+    checkInterrupt();
+    try {
+        Db * db = getDb(table);
+        Dbt kt((void *) key.c_str(), key.length());
+        Dbt dt((void *) data.c_str(), data.length());
+        db->put(txn.txn, &kt, &dt, 0);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Database::setStrings(const Transaction & txn, TableId table,
+    const string & key, const Strings & data, bool deleteEmpty)
+{
+    if (deleteEmpty && data.size() == 0)
+        delPair(txn, table, key);
+    else
+        setString(txn, table, key, packStrings(data));
+}
+
+
+void Database::delPair(const Transaction & txn, TableId table,
+    const string & key)
+{
+    checkInterrupt();
+    try {
+        Db * db = getDb(table);
+        Dbt kt((void *) key.c_str(), key.length());
+        db->del(txn.txn, &kt, 0);
+        /* Non-existence of a pair with the given key is not an
+           error. */
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+void Database::enumTable(const Transaction & txn, TableId table,
+    Strings & keys, const string & keyPrefix)
+{
+    try {
+        Db * db = getDb(table);
+
+        Dbc * dbc;
+        db->cursor(txn.txn, &dbc, 0);
+        DestroyDbc destroyDbc(dbc);
+
+        Dbt kt, dt;
+        u_int32_t flags = DB_NEXT;
+
+        if (!keyPrefix.empty()) {
+            flags = DB_SET_RANGE;
+            kt = Dbt((void *) keyPrefix.c_str(), keyPrefix.size());
+        }
+
+        while (dbc->get(&kt, &dt, flags) != DB_NOTFOUND) {
+            checkInterrupt();
+            string data((char *) kt.get_data(), kt.get_size());
+            if (!keyPrefix.empty() &&
+                string(data, 0, keyPrefix.size()) != keyPrefix)
+                break;
+            keys.push_back(data);
+            flags = DB_NEXT;
+        }
+
+    } catch (DbException e) { rethrow(e); }
+}
+
+ 
+void Database::clearTable(const Transaction & txn, TableId table)
+{
+    try {
+        Db * db = getDb(table);
+        u_int32_t count;
+        db->truncate(txn.txn, &count, 0);
+    } catch (DbException e) { rethrow(e); }
+}
+
+
+}
+
+#endif
--- a/src/libstore/db.hh
+++ b/src/libstore/db.hh
@@ -0,0 +1,107 @@
+#ifndef __DB_H
+#define __DB_H
+
+#include "types.hh"
+
+#include <map>
+
+
+/* Defined externally. */
+class DbTxn;
+class DbEnv;
+class Db;
+
+
+namespace nix {
+
+
+class Database;
+
+
+class Transaction
+{
+    friend class Database;
+
+private:
+    DbTxn * txn;
+    
+public:
+    Transaction();
+    Transaction(Database & _db);
+    ~Transaction();
+
+    void begin(Database & db);
+    void abort();
+    void commit();
+
+    void moveTo(Transaction & t);
+};
+
+
+#define noTxn Transaction()
+
+
+typedef unsigned int TableId; /* table handles */
+
+
+class Database
+{
+    friend class Transaction;
+
+private:
+    DbEnv * env;
+
+    TableId nextId;
+    std::map<TableId, Db *> tables;
+
+    void requireEnv();
+
+    Db * getDb(TableId table);
+
+    void open2(const string & path, bool removeOldEnv);
+    
+public:
+    Database();
+    ~Database();
+    
+    void open(const string & path);
+    void close();
+
+    TableId openTable(const string & table, bool sorted = false);
+    void closeTable(TableId table);
+    void deleteTable(const string & table);
+
+    bool queryString(const Transaction & txn, TableId table, 
+        const string & key, string & data);
+
+    bool queryStrings(const Transaction & txn, TableId table, 
+        const string & key, Strings & data);
+
+    void setString(const Transaction & txn, TableId table,
+        const string & key, const string & data);
+
+    void setStrings(const Transaction & txn, TableId table,
+        const string & key, const Strings & data,
+        bool deleteEmpty = true);
+
+    void delPair(const Transaction & txn, TableId table,
+        const string & key);
+
+    void enumTable(const Transaction & txn, TableId table,
+        Strings & keys, const string & keyPrefix = "");
+
+    void clearTable(const Transaction & txn, TableId table);
+};
+
+
+class DbNoPermission : public Error
+{
+public:
+    DbNoPermission(const format & f) : Error(f) { };
+};
+
+ 
+}
+
+
+#endif /* !__DB_H */
--- a/src/libstore/derivations-ast.def
+++ b/src/libstore/derivations-ast.def
@@ -0,0 +1,10 @@
+init initDerivationsHelpers
+
+Derive | ATermList ATermList ATermList string string ATermList ATermList | ATerm |
+
+| string string | ATerm | EnvBinding |
+| string ATermList | ATerm | DerivationInput |
+| string string string string | ATerm | DerivationOutput |
+
+Closure | ATermList ATermList | ATerm | OldClosure |
+| string ATermList | ATerm | OldClosureElem |
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -1,12 +1,22 @@
 #include "derivations.hh"
 #include "store-api.hh"
+#include "aterm.hh"
 #include "globals.hh"
 #include "util.hh"

+#include "derivations-ast.hh"
+#include "derivations-ast.cc"
+

 namespace nix {


+Hash hashTerm(ATerm t)
+{
+    return hashString(htSHA256, atPrint(t));
+}
+
+
 Path writeDerivation(const Derivation & drv, const string & name)
 {
    PathSet references;
@@ -17,151 +27,137 @@ Path writeDerivation(const Derivation & drv, const string & name)
       (that can be missing (of course) and should not necessarily be
       held during a garbage collection). */
    string suffix = name + drvExtension;
-    string contents = unparseDerivation(drv);
+    string contents = atPrint(unparseDerivation(drv));
    return readOnlyMode
        ? computeStorePathForText(suffix, contents, references)
        : store->addTextToStore(suffix, contents, references);
 }


-static Path parsePath(std::istream & str)
+static void checkPath(const string & s)
 {
-    string s = parseString(str);
    if (s.size() == 0 || s[0] != '/')
        throw Error(format("bad path `%1%' in derivation") % s);
-    return s;
 }
    

-static StringSet parseStrings(std::istream & str, bool arePaths)
+static void parseStrings(ATermList paths, StringSet & out, bool arePaths)
 {
-    StringSet res;
-    while (!endOfList(str))
-        res.insert(arePaths ? parsePath(str) : parseString(str));
-    return res;
+    for (ATermIterator i(paths); i; ++i) {
+        if (ATgetType(*i) != AT_APPL)
+            throw badTerm("not a path", *i);
+        string s = aterm2String(*i);
+        if (arePaths) checkPath(s);
+        out.insert(s);
+    }
 }
-    

-Derivation parseDerivation(const string & s)
+
+/* Shut up warnings. */
+void throwBadDrv(ATerm t) __attribute__ ((noreturn));
+
+void throwBadDrv(ATerm t) 
+{
+    throw badTerm("not a valid derivation", t);
+}
+
+
+Derivation parseDerivation(ATerm t)
 {
    Derivation drv;
-    std::istringstream str(s);
-    expect(str, "Derive([");
+    ATermList outs, inDrvs, inSrcs, args, bnds;
+    ATerm builder, platform;

-    /* Parse the list of outputs. */
-    while (!endOfList(str)) {
+    if (!matchDerive(t, outs, inDrvs, inSrcs, platform, builder, args, bnds))
+        throwBadDrv(t);
+
+    for (ATermIterator i(outs); i; ++i) {
+        ATerm id, path, hashAlgo, hash;
+        if (!matchDerivationOutput(*i, id, path, hashAlgo, hash))
+            throwBadDrv(t);
        DerivationOutput out;
-        expect(str, "("); string id = parseString(str);
-        expect(str, ","); out.path = parsePath(str);
-        expect(str, ","); out.hashAlgo = parseString(str);
-        expect(str, ","); out.hash = parseString(str);
-        expect(str, ")");
-        drv.outputs[id] = out;
+        out.path = aterm2String(path);
+        checkPath(out.path);
+        out.hashAlgo = aterm2String(hashAlgo);
+        out.hash = aterm2String(hash);
+        drv.outputs[aterm2String(id)] = out;
    }

-    /* Parse the list of input derivations. */
-    expect(str, ",[");
-    while (!endOfList(str)) {
-        expect(str, "(");
-        Path drvPath = parsePath(str);
-        expect(str, ",[");
-        drv.inputDrvs[drvPath] = parseStrings(str, false);
-        expect(str, ")");
-    }
-
-    expect(str, ",["); drv.inputSrcs = parseStrings(str, true);
-    expect(str, ","); drv.platform = parseString(str);
-    expect(str, ","); drv.builder = parseString(str);
-
-    /* Parse the builder arguments. */
-    expect(str, ",[");
-    while (!endOfList(str))
-        drv.args.push_back(parseString(str));
-
-    /* Parse the environment variables. */
-    expect(str, ",[");
-    while (!endOfList(str)) {
-        expect(str, "("); string name = parseString(str);
-        expect(str, ","); string value = parseString(str);
-        expect(str, ")");
-        drv.env[name] = value;
+    for (ATermIterator i(inDrvs); i; ++i) {
+        ATerm drvPath;
+        ATermList ids;
+        if (!matchDerivationInput(*i, drvPath, ids))
+            throwBadDrv(t);
+        Path drvPath2 = aterm2String(drvPath);
+        checkPath(drvPath2);
+        StringSet ids2;
+        parseStrings(ids, ids2, false);
+        drv.inputDrvs[drvPath2] = ids2;
    }
    
-    expect(str, ")");
+    parseStrings(inSrcs, drv.inputSrcs, true);
+
+    drv.builder = aterm2String(builder);
+    drv.platform = aterm2String(platform);
+    
+    for (ATermIterator i(args); i; ++i) {
+        if (ATgetType(*i) != AT_APPL)
+            throw badTerm("string expected", *i);
+        drv.args.push_back(aterm2String(*i));
+    }
+
+    for (ATermIterator i(bnds); i; ++i) {
+        ATerm s1, s2;
+        if (!matchEnvBinding(*i, s1, s2))
+            throw badTerm("tuple of strings expected", *i);
+        drv.env[aterm2String(s1)] = aterm2String(s2);
+    }
+
    return drv;
 }


-static void printString(string & res, const string & s)
+ATerm unparseDerivation(const Derivation & drv)
 {
-    res += '"';
-    for (const char * i = s.c_str(); *i; i++)
-        if (*i == '\"' || *i == '\\') { res += "\\"; res += *i; }
-        else if (*i == '\n') res += "\\n";
-        else if (*i == '\r') res += "\\r";
-        else if (*i == '\t') res += "\\t";
-        else res += *i;
-    res += '"';
-}
+    ATermList outputs = ATempty;
+    for (DerivationOutputs::const_reverse_iterator i = drv.outputs.rbegin();
+         i != drv.outputs.rend(); ++i)
+        outputs = ATinsert(outputs,
+            makeDerivationOutput(
+                toATerm(i->first),
+                toATerm(i->second.path),
+                toATerm(i->second.hashAlgo),
+                toATerm(i->second.hash)));

-
-template<class ForwardIterator>
-static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
-{
-    res += '[';
-    bool first = true;
-    for ( ; i != j; ++i) {
-        if (first) first = false; else res += ',';
-        printString(res, *i);
-    }
-    res += ']';
-}
-
-
-string unparseDerivation(const Derivation & drv)
-{
-    string s;
-    s.reserve(65536);
-    s += "Derive([";
-
-    bool first = true;
-    foreach (DerivationOutputs::const_iterator, i, drv.outputs) {
-        if (first) first = false; else s += ',';
-        s += '('; printString(s, i->first);
-        s += ','; printString(s, i->second.path);
-        s += ','; printString(s, i->second.hashAlgo);
-        s += ','; printString(s, i->second.hash);
-        s += ')';
-    }
-
-    s += "],[";
-    first = true;
-    foreach (DerivationInputs::const_iterator, i, drv.inputDrvs) {
-        if (first) first = false; else s += ',';
-        s += '('; printString(s, i->first);
-        s += ','; printStrings(s, i->second.begin(), i->second.end());
-        s += ')';
-    }
-
-    s += "],";
-    printStrings(s, drv.inputSrcs.begin(), drv.inputSrcs.end());
+    ATermList inDrvs = ATempty;
+    for (DerivationInputs::const_reverse_iterator i = drv.inputDrvs.rbegin();
+         i != drv.inputDrvs.rend(); ++i)
+        inDrvs = ATinsert(inDrvs,
+            makeDerivationInput(
+                toATerm(i->first),
+                toATermList(i->second)));
    
-    s += ','; printString(s, drv.platform);
-    s += ','; printString(s, drv.builder);
-    s += ','; printStrings(s, drv.args.begin(), drv.args.end());
+    ATermList args = ATempty;
+    for (Strings::const_reverse_iterator i = drv.args.rbegin();
+         i != drv.args.rend(); ++i)
+        args = ATinsert(args, toATerm(*i));

-    s += ",[";
-    first = true;
-    foreach (StringPairs::const_iterator, i, drv.env) {
-        if (first) first = false; else s += ',';
-        s += '('; printString(s, i->first);
-        s += ','; printString(s, i->second);
-        s += ')';
-    }
-    
-    s += "])";
-    
-    return s;
+    ATermList env = ATempty;
+    for (StringPairs::const_reverse_iterator i = drv.env.rbegin();
+         i != drv.env.rend(); ++i)
+        env = ATinsert(env,
+            makeEnvBinding(
+                toATerm(i->first),
+                toATerm(i->second)));
+
+    return makeDerive(
+        outputs,
+        inDrvs,
+        toATermList(drv.inputSrcs),
+        toATerm(drv.platform),
+        toATerm(drv.builder),
+        args,
+        env);
 }


--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -1,6 +1,8 @@
 #ifndef __DERIVATIONS_H
 #define __DERIVATIONS_H

+typedef struct _ATerm * ATerm;
+
 #include "hash.hh"

 #include <map>
@@ -51,14 +53,17 @@ struct Derivation
 };


+/* Hash an aterm. */
+Hash hashTerm(ATerm t);
+
 /* Write a derivation to the Nix store, and return its path. */
 Path writeDerivation(const Derivation & drv, const string & name);

 /* Parse a derivation. */
-Derivation parseDerivation(const string & s);
+Derivation parseDerivation(ATerm t);

-/* Print a derivation. */
-string unparseDerivation(const Derivation & drv);
+/* Parse a derivation. */
+ATerm unparseDerivation(const Derivation & drv);

 /* Check whether a file name ends with the extensions for
   derivations. */
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -7,7 +7,6 @@

 #include <functional>
 #include <queue>
-#include <algorithm>

 #include <sys/types.h>
 #include <sys/stat.h>
@@ -15,6 +14,11 @@
 #include <fcntl.h>
 #include <unistd.h>

+#ifdef __CYGWIN__
+#include <windows.h>
+#include <sys/cygwin.h>
+#endif
+

 namespace nix {

@@ -174,6 +178,15 @@ void LocalStore::addTempRoot(const Path & path)

            fdGCLock.close();
      
+	    /* Note that on Cygwin a lot of the following complexity
+	       is unnecessary, since we cannot delete open lock
+	       files.  If we have the lock file open, then it's valid;
+	       if we can delete it, then it wasn't in use any more. 
+
+	       Also note that on Cygwin we cannot "upgrade" a lock
+	       from a read lock to a write lock. */
+
+#ifndef __CYGWIN__
            debug(format("acquiring read lock on `%1%'") % fnTempRoots);
            lockFile(fdTempRoots, ltRead, true);

@@ -187,6 +200,10 @@ void LocalStore::addTempRoot(const Path & path)
            /* The garbage collector deleted this file before we could
               get a lock.  (It won't delete the file after we get a
               lock.)  Try again. */
+
+#else
+            break;
+#endif
        }

    }
@@ -199,9 +216,14 @@ void LocalStore::addTempRoot(const Path & path)
    string s = path + '\0';
    writeFull(fdTempRoots, (const unsigned char *) s.c_str(), s.size());

+#ifndef __CYGWIN__
    /* Downgrade to a read lock. */
    debug(format("downgrading to read lock on `%1%'") % fnTempRoots);
    lockFile(fdTempRoots, ltRead, true);
+#else
+    debug(format("releasing write lock on `%1%'") % fnTempRoots);
+    lockFile(fdTempRoots, ltNone, true);
+#endif
 }


@@ -229,6 +251,19 @@ static void readTempRoots(PathSet & tempRoots, FDs & fds)
        Path path = (format("%1%/%2%/%3%") % nixStateDir % tempRootsDir % *i).str();

        debug(format("reading temporary root file `%1%'") % path);
+
+#ifdef __CYGWIN__
+	/* On Cygwin we just try to delete the lock file. */
+	char win32Path[MAX_PATH];
+	cygwin_conv_to_full_win32_path(path.c_str(), win32Path);
+	if (DeleteFile(win32Path)) {
+            printMsg(lvlError, format("removed stale temporary roots file `%1%'")
+                % path);
+            continue;
+        } else
+            debug(format("delete of `%1%' failed: %2%") % path % GetLastError());
+#endif
+
        FDPtr fd(new AutoCloseFD(open(path.c_str(), O_RDWR, 0666)));
        if (*fd == -1) {
            /* It's okay if the file has disappeared. */
@@ -240,6 +275,7 @@ static void readTempRoots(PathSet & tempRoots, FDs & fds)
        //FDPtr fd(new AutoCloseFD(openLockFile(path, false)));
        //if (*fd == -1) continue;

+#ifndef __CYGWIN__
        /* Try to acquire a write lock without blocking.  This can
           only succeed if the owning process has died.  In that case
           we don't care about its temporary roots. */
@@ -250,6 +286,7 @@ static void readTempRoots(PathSet & tempRoots, FDs & fds)
            writeFull(*fd, (const unsigned char *) "d", 1);
            continue;
        }
+#endif

        /* Acquire a read lock.  This will prevent the owning process
           from upgrading to a write lock, therefore it will block in
@@ -364,7 +401,7 @@ static void addAdditionalRoots(PathSet & roots)
        if (isInStore(*i)) {
            Path path = toStorePath(*i);
            if (roots.find(path) == roots.end() && store->isValidPath(path)) {
-                debug(format("got additional root `%1%'") % path);
+                debug(format("found additional root `%1%'") % path);
                roots.insert(path);
            }
        }
@@ -402,218 +439,147 @@ Paths topoSortPaths(const PathSet & paths)
 }


+static time_t lastFileAccessTime(const Path & path)
+{
+    checkInterrupt();
+    
+    struct stat st;
+    if (lstat(path.c_str(), &st) == -1)
+        throw SysError(format("statting `%1%'") % path);
+
+    if (S_ISDIR(st.st_mode)) {
+        time_t last = 0;
+	Strings names = readDirectory(path);
+	foreach (Strings::iterator, i, names) {
+            time_t t = lastFileAccessTime(path + "/" + *i);
+            if (t > last) last = t;
+        }
+        return last;
+    }
+
+    else if (S_ISLNK(st.st_mode)) return 0;
+
+    else return st.st_atime;
+}
+
+
 struct GCLimitReached { };


-struct LocalStore::GCState
+void LocalStore::gcPath(const GCOptions & options, GCResults & results, 
+    const Path & path)
 {
-    GCOptions options;
-    GCResults & results;
-    PathSet roots;
-    PathSet tempRoots;
-    PathSet deleted;
-    PathSet live;
-    PathSet busy;
-    bool gcKeepOutputs;
-    bool gcKeepDerivations;
+    results.paths.insert(path);

-    bool drvsIndexed;
-    typedef std::multimap<string, Path> DrvsByName;
-    DrvsByName drvsByName; // derivation paths hashed by name attribute
+    if (!pathExists(path)) return;
+                
+    /* Okay, it's safe to delete. */
+    unsigned long long bytesFreed, blocksFreed;
+    deleteFromStore(path, bytesFreed, blocksFreed);
+    results.bytesFreed += bytesFreed;
+    results.blocksFreed += blocksFreed;

-    GCState(GCResults & results_) : results(results_), drvsIndexed(false)
+    if (options.maxFreed && results.bytesFreed > options.maxFreed) {
+        printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % options.maxFreed);
+        throw GCLimitReached();
+    }
+
+    if (options.maxLinks) {
+        struct stat st;
+        if (stat(nixStore.c_str(), &st) == -1)
+            throw SysError(format("statting `%1%'") % nixStore);
+        if (st.st_nlink < options.maxLinks) {
+            printMsg(lvlInfo, format("link count on the store has dropped below %1%; stopping") % options.maxLinks);
+            throw GCLimitReached();
+        }
+    }
+}
+
+
+void LocalStore::gcPathRecursive(const GCOptions & options,
+    GCResults & results, PathSet & done, const Path & path)
+{
+    if (done.find(path) != done.end()) return;
+    done.insert(path);
+
+    startNest(nest, lvlDebug, format("looking at `%1%'") % path);
+        
+    /* Delete all the referrers first.  They must be garbage too,
+       since if they were live, then the current path would also be
+       live.  Note that deleteFromStore() below still makes sure that
+       the referrer set has become empty, just in case.  (However that
+       doesn't guard against deleting top-level paths that are only
+       reachable from GC roots.) */
+    PathSet referrers;
+    if (isValidPath(path))
+        queryReferrers(path, referrers);
+    foreach (PathSet::iterator, i, referrers)
+        if (*i != path) gcPathRecursive(options, results, done, *i);
+
+    printMsg(lvlInfo, format("deleting `%1%'") % path);
+            
+    gcPath(options, results, path);
+}
+
+
+struct CachingAtimeComparator : public std::binary_function<Path, Path, bool> 
+{
+    std::map<Path, time_t> cache;
+
+    time_t lookup(const Path & p)
    {
+        std::map<Path, time_t>::iterator i = cache.find(p);
+        if (i != cache.end()) return i->second;
+        debug(format("computing atime of `%1%'") % p);
+        cache[p] = lastFileAccessTime(p);
+        assert(cache.find(p) != cache.end());
+        return cache[p];
+    }
+        
+    bool operator () (const Path & p1, const Path & p2)
+    {
+        return lookup(p2) < lookup(p1);
    }
 };


-static bool doDelete(GCOptions::GCAction action)
+static string showTime(const string & format, time_t t)
 {
-    return action == GCOptions::gcDeleteDead
-        || action == GCOptions::gcDeleteSpecific;
+    char s[128];
+    strftime(s, sizeof s, format.c_str(), localtime(&t));
+    return string(s);
 }


-bool LocalStore::isActiveTempFile(const GCState & state,
-    const Path & path, const string & suffix)
+static bool isLive(const Path & path, const PathSet & livePaths,
+    const PathSet & tempRoots, const PathSet & tempRootsClosed)
 {
-    return hasSuffix(path, suffix)
-        && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
-}
+    if (livePaths.find(path) != livePaths.end() ||
+        tempRootsClosed.find(path) != tempRootsClosed.end()) return true;

+    /* A lock file belonging to a path that we're building right
+       now isn't garbage. */
+    if (hasSuffix(path, ".lock") && tempRoots.find(string(path, 0, path.size() - 5)) != tempRoots.end())
+        return true;

-/* Return all the derivations in the Nix store that have `path' as an
-   output.  This function assumes that derivations have the same name
-   as their outputs. */
-PathSet LocalStore::findDerivers(GCState & state, const Path & path)
-{
-    PathSet derivers;
+    /* Don't delete .chroot directories for derivations that are
+       currently being built. */
+    if (hasSuffix(path, ".chroot") && tempRoots.find(string(path, 0, path.size() - 7)) != tempRoots.end())
+        return true;

-    Path deriver = queryDeriver(path);
-    if (deriver != "") derivers.insert(deriver);
-
-    if (!state.drvsIndexed) {
-        Paths entries = readDirectory(nixStore);
-        foreach (Paths::iterator, i, entries)
-            if (isDerivation(*i))
-                state.drvsByName.insert(std::pair<string, Path>(
-                        getNameOfStorePath(*i), nixStore + "/" + *i));
-        state.drvsIndexed = true;
-    }
-    
-    string name = getNameOfStorePath(path);
-
-    // Urgh, I should have used Haskell...
-    std::pair<GCState::DrvsByName::iterator, GCState::DrvsByName::iterator> range =
-        state.drvsByName.equal_range(name);
-
-    for (GCState::DrvsByName::iterator i = range.first; i != range.second; ++i)
-        if (isValidPath(i->second)) {
-            Derivation drv = derivationFromPath(i->second);
-            foreach (DerivationOutputs::iterator, j, drv.outputs)
-                if (j->second.path == path) derivers.insert(i->second);
-        }
-
-    return derivers;
-}
-
-    
-bool LocalStore::tryToDelete(GCState & state, const Path & path)
-{
-    if (!pathExists(path)) return true;
-    if (state.deleted.find(path) != state.deleted.end()) return true;
-    if (state.live.find(path) != state.live.end()) return false;
-
-    startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path);
-
-    if (state.roots.find(path) != state.roots.end()) {
-        printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path);
-        goto isLive;
-    }
-
-    if (isValidPath(path)) {
-
-        /* Recursively try to delete the referrers of this path.  If
-           any referrer can't be deleted, then this path can't be
-           deleted either. */
-        PathSet referrers;
-        queryReferrers(path, referrers);
-        foreach (PathSet::iterator, i, referrers)
-            if (*i != path && !tryToDelete(state, *i)) {
-                printMsg(lvlDebug, format("cannot delete `%1%' because it has live referrers") % path);
-                goto isLive;
-            }
-
-        /* If gc-keep-derivations is set and this is a derivation,
-           then don't delete the derivation if any of the outputs are
-           live. */
-        if (state.gcKeepDerivations && isDerivation(path)) {
-            Derivation drv = derivationFromPath(path);
-            foreach (DerivationOutputs::iterator, i, drv.outputs)
-                if (!tryToDelete(state, i->second.path)) {
-                    printMsg(lvlDebug, format("cannot delete derivation `%1%' because its output is alive") % path);
-                    goto isLive;
-                }
-        }
-
-        /* If gc-keep-derivations and gc-keep-outputs are both set,
-           it's possible that the path has already been deleted (due
-           to the recursion below), so bail out. */
-        if (!pathExists(path)) return true;
-
-        /* If gc-keep-outputs is set, then don't delete this path if
-           its deriver is not garbage.  !!! Nix does not reliably
-           store derivers, so we have to look at all derivations to
-           determine which of them derive `path'.  Since this makes
-           the garbage collector very slow to start on large Nix
-           stores, here we just look for all derivations that have the
-           same name as `path' (where the name is the part of the
-           filename after the hash, i.e. the `name' attribute of the
-           derivation).  This is somewhat hacky: currently, the
-           deriver of a path always has the same name as the output,
-           but this might change in the future. */
-        if (state.gcKeepOutputs) {
-            PathSet derivers = findDerivers(state, path);
-            foreach (PathSet::iterator, deriver, derivers) {
-                /* Break an infinite recursion if gc-keep-derivations
-                   and gc-keep-outputs are both set by tentatively
-                   assuming that this path is garbage.  This is a safe
-                   assumption because at this point, the only thing
-                   that can prevent it from being garbage is the
-                   deriver.  Since tryToDelete() works "upwards"
-                   through the dependency graph, it won't encouter
-                   this path except in the call to tryToDelete() in
-                   the gc-keep-derivation branch. */
-                state.deleted.insert(path);
-                if (!tryToDelete(state, *deriver)) {
-                    state.deleted.erase(path);
-                    printMsg(lvlDebug, format("cannot delete `%1%' because its deriver `%2%' is alive") % path % *deriver);
-                    goto isLive;
-                }
-            }
-        }
-    }
-
-    else {
-
-        /* A lock file belonging to a path that we're building right
-           now isn't garbage. */
-        if (isActiveTempFile(state, path, ".lock")) return false;
-
-        /* Don't delete .chroot directories for derivations that are
-           currently being built. */
-        if (isActiveTempFile(state, path, ".chroot")) return false;
-
-    }
-
-    /* The path is garbage, so delete it. */
-    if (doDelete(state.options.action)) {
-        printMsg(lvlInfo, format("deleting `%1%'") % path);
-
-        unsigned long long bytesFreed, blocksFreed;
-        deleteFromStore(path, bytesFreed, blocksFreed);
-        state.results.bytesFreed += bytesFreed;
-        state.results.blocksFreed += blocksFreed;
-
-        if (state.options.maxFreed && state.results.bytesFreed > state.options.maxFreed) {
-            printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % state.options.maxFreed);
-            throw GCLimitReached();
-        }
-
-        if (state.options.maxLinks) {
-            struct stat st;
-            if (stat(nixStore.c_str(), &st) == -1)
-                throw SysError(format("statting `%1%'") % nixStore);
-            if (st.st_nlink < state.options.maxLinks) {
-                printMsg(lvlInfo, format("link count on the store has dropped below %1%; stopping") % state.options.maxLinks);
-                throw GCLimitReached();
-            }
-        }
-        
-    } else
-        printMsg(lvlTalkative, format("would delete `%1%'") % path);
-    
-    state.deleted.insert(path);
-    if (state.options.action != GCOptions::gcReturnLive)
-        state.results.paths.insert(path);
-    return true;
-
- isLive:
-    state.live.insert(path);
-    if (state.options.action == GCOptions::gcReturnLive)
-        state.results.paths.insert(path);
    return false;
 }


 void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 {
-    GCState state(results);
-    state.options = options;    
-    
-    state.gcKeepOutputs = queryBoolSetting("gc-keep-outputs", false);
-    state.gcKeepDerivations = queryBoolSetting("gc-keep-derivations", true);
-    
+    bool gcKeepOutputs =
+        queryBoolSetting("gc-keep-outputs", false);
+    bool gcKeepDerivations =
+        queryBoolSetting("gc-keep-derivations", true);
+    int gcKeepOutputsThreshold = 
+        queryIntSetting ("gc-keep-outputs-threshold", defaultGcLevel);
+
    /* Acquire the global GC root.  This prevents
       a) New roots from being added.
       b) Processes from creating new temporary root files. */
@@ -624,60 +590,198 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
    printMsg(lvlError, format("finding garbage collector roots..."));
    Roots rootMap = options.ignoreLiveness ? Roots() : nix::findRoots(true);

-    foreach (Roots::iterator, i, rootMap) state.roots.insert(i->second);
+    PathSet roots;
+    foreach (Roots::iterator, i, rootMap) roots.insert(i->second);

    /* Add additional roots returned by the program specified by the
       NIX_ROOT_FINDER environment variable.  This is typically used
       to add running programs to the set of roots (to prevent them
       from being garbage collected). */
    if (!options.ignoreLiveness)
-        addAdditionalRoots(state.roots);
+        addAdditionalRoots(roots);
+
+    if (options.action == GCOptions::gcReturnRoots) {
+        results.paths = roots;
+        return;
+    }
+
+    /* Determine the live paths which is just the closure of the
+       roots under the `references' relation. */
+    printMsg(lvlError, format("computing live paths..."));
+    PathSet livePaths;
+    foreach (PathSet::const_iterator, i, roots)
+        computeFSClosure(canonPath(*i), livePaths);
+
+    if (gcKeepDerivations) {
+        foreach (PathSet::iterator, i, livePaths) {
+            /* Note that the deriver need not be valid (e.g., if we
+               previously ran the collector with `gcKeepDerivations'
+               turned off). */
+            Path deriver = queryDeriver(*i);
+            if (deriver != "" && isValidPath(deriver))
+                computeFSClosure(deriver, livePaths);
+        }
+    }
+
+    if (gcKeepOutputs) {
+        /* Hmz, identical to storePathRequisites in nix-store. */
+        foreach (PathSet::iterator, i, livePaths)
+            if (isDerivation(*i)) {
+                Derivation drv = derivationFromPath(*i);
+
+		string gcLevelStr = drv.env["__gcLevel"];
+		int gcLevel;
+		if (!string2Int(gcLevelStr, gcLevel))
+		    gcLevel = defaultGcLevel;
+		
+		if (gcLevel >= gcKeepOutputsThreshold)    
+		    foreach (DerivationOutputs::iterator, j, drv.outputs)
+			if (isValidPath(j->second.path))
+			    computeFSClosure(j->second.path, livePaths);
+            }
+    }
+
+    if (options.action == GCOptions::gcReturnLive) {
+        results.paths = livePaths;
+        return;
+    }

    /* Read the temporary roots.  This acquires read locks on all
       per-process temporary root files.  So after this point no paths
       can be added to the set of temporary roots. */
+    PathSet tempRoots;
    FDs fds;
-    readTempRoots(state.tempRoots, fds);
-    state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
+    readTempRoots(tempRoots, fds);
+
+    /* Close the temporary roots.  Note that we *cannot* do this in
+       readTempRoots(), because there we may not have all locks yet,
+       meaning that an invalid path can become valid (and thus add to
+       the references graph) after we have added it to the closure
+       (and computeFSClosure() assumes that the presence of a path
+       means that it has already been closed). */
+    PathSet tempRootsClosed;
+    foreach (PathSet::iterator, i, tempRoots)
+        if (isValidPath(*i))
+            computeFSClosure(*i, tempRootsClosed);
+        else
+            tempRootsClosed.insert(*i);

    /* After this point the set of roots or temporary roots cannot
       increase, since we hold locks on everything.  So everything
-       that is not reachable from `roots'. */
-
-    /* Now either delete all garbage paths, or just the specified
-       paths (for gcDeleteSpecific). */
-
-    if (options.action == GCOptions::gcDeleteSpecific) {
+       that is not currently in in `livePaths' or `tempRootsClosed'
+       can be deleted. */
+    
+    /* Read the Nix store directory to find all currently existing
+       paths and filter out all live paths. */
+    printMsg(lvlError, format("reading the Nix store..."));
+    PathSet storePaths;
+    
+    if (options.action != GCOptions::gcDeleteSpecific) {
+        Paths entries = readDirectory(nixStore);
+        foreach (Paths::iterator, i, entries) {
+            Path path = canonPath(nixStore + "/" + *i);
+            if (!isLive(path, livePaths, tempRoots, tempRootsClosed)) storePaths.insert(path);
+        }
+    }

+    else {
        foreach (PathSet::iterator, i, options.pathsToDelete) {
            assertStorePath(*i);
-            if (!tryToDelete(state, *i))
+            storePaths.insert(*i);
+            if (isLive(*i, livePaths, tempRoots, tempRootsClosed))
                throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
        }
-        
-    } else {
-        
-        printMsg(lvlError, format("reading the Nix store..."));
-        Paths entries = readDirectory(nixStore);
+    }

-        /* Randomise the order in which we delete entries to make the
-           collector less biased towards deleting paths that come
-           alphabetically first (e.g. /nix/store/000...).  This
-           matters when using --max-freed etc. */
-        vector<Path> entries_(entries.begin(), entries.end());
-        random_shuffle(entries_.begin(), entries_.end());
+    if (options.action == GCOptions::gcReturnDead) {
+        results.paths.insert(storePaths.begin(), storePaths.end());
+        return;
+    }

-        if (doDelete(state.options.action))
+    /* Delete all dead store paths (or until one of the stop
+       conditions is reached). */
+
+    PathSet done;
+    try {
+
+        if (!options.useAtime) {
+            /* Delete the paths, respecting the partial ordering
+               determined by the references graph. */
            printMsg(lvlError, format("deleting garbage..."));
-        else
-            printMsg(lvlError, format("determining live/dead paths..."));
-    
-        try {
-            foreach (vector<Path>::iterator, i, entries_)
-                tryToDelete(state, canonPath(nixStore + "/" + *i));
-        } catch (GCLimitReached & e) {
+            foreach (PathSet::iterator, i, storePaths)
+                gcPathRecursive(options, results, done, *i);
        }
-    }        
+
+        else {
+
+            /* Delete in order of ascending last access time, still
+               maintaining the partial ordering of the reference
+               graph.  Note that we can't use a topological sort for
+               this because that takes time O(V+E), and in this case
+               E=O(V^2) (i.e. the graph is dense because of the edges
+               due to the atime ordering).  So instead we put all
+               deletable paths in a priority queue (ordered by atime),
+               and after deleting a path, add additional paths that
+               have become deletable to the priority queue. */
+
+            CachingAtimeComparator atimeComp;
+
+            /* Create a priority queue that orders paths by ascending
+               atime.  This is why C++ needs type inferencing... */
+            std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> > prioQueue =
+                std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> >(binary_function_ref_adapter<CachingAtimeComparator>(&atimeComp));
+
+           /* Initially put the paths that are invalid or have no
+              referrers into the priority queue. */
+            printMsg(lvlError, format("finding deletable paths..."));
+            foreach (PathSet::iterator, i, storePaths) {
+                checkInterrupt();
+                /* We can safely delete a path if it's invalid or
+                   it has no referrers.  Note that all the invalid
+                   paths will be deleted in the first round. */
+                if (isValidPath(*i)) {
+                    if (queryReferrersNoSelf(*i).empty()) prioQueue.push(*i);
+                } else prioQueue.push(*i);
+            }
+
+            debug(format("%1% initially deletable paths") % prioQueue.size());
+
+            /* Now delete everything in the order of the priority
+               queue until nothing is left. */
+            printMsg(lvlError, format("deleting garbage..."));
+            while (!prioQueue.empty()) {
+                checkInterrupt();
+                Path path = prioQueue.top(); prioQueue.pop();
+
+                if (options.maxAtime != (time_t) -1 &&
+                    atimeComp.lookup(path) > options.maxAtime)
+                    continue;
+                
+                printMsg(lvlInfo, format("deleting `%1%' (last accessed %2%)") % path % showTime("%F %H:%M:%S", atimeComp.lookup(path)));
+
+                PathSet references;
+                if (isValidPath(path)) references = queryReferencesNoSelf(path);
+
+                gcPath(options, results, path);
+
+                /* For each reference of the current path, see if the
+                   reference has now become deletable (i.e. is in the
+                   set of dead paths and has no referrers left).  If
+                   so add it to the priority queue. */
+                foreach (PathSet::iterator, i, references) {
+                    if (storePaths.find(*i) != storePaths.end() &&
+                        queryReferrersNoSelf(*i).empty())
+                    {
+                        debug(format("path `%1%' has become deletable") % *i);
+                        prioQueue.push(*i);
+                    }
+                }
+            }
+            
+        }
+        
+    } catch (GCLimitReached & e) {
+    }
 }


--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -13,6 +13,7 @@ string nixDataDir = "/UNINIT";
 string nixLogDir = "/UNINIT";
 string nixStateDir = "/UNINIT";
 string nixDBPath = "/UNINIT";
+string nixCacheFile = "/UNINIT";
 string nixConfDir = "/UNINIT";
 string nixLibexecDir = "/UNINIT";
 string nixBinDir = "/UNINIT";
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -24,6 +24,9 @@ extern string nixStateDir;
 /* nixDBPath is the path name of our Berkeley DB environment. */
 extern string nixDBPath;

+/* nixCacheFile is the path name of the normal form cache. */
+extern string nixCacheFile;
+
 /* nixConfDir is the directory where configuration files are
   stored. */
 extern string nixConfDir;
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -3,6 +3,8 @@
 #include "globals.hh"
 #include "archive.hh"
 #include "pathlocks.hh"
+#include "aterm.hh"
+#include "derivations-ast.hh"
 #include "worker-protocol.hh"
    
 #include <iostream>
@@ -14,7 +16,6 @@
 #include <utime.h>
 #include <fcntl.h>
 #include <errno.h>
-#include <stdio.h>


 namespace nix {
@@ -46,21 +47,8 @@ LocalStore::LocalStore()
    
    if (readOnlyMode) return;

-    /* Create missing state directories if they don't already exist. */
    createDirs(nixStore);
-    createDirs(nixDBPath + "/info");
-    createDirs(nixDBPath + "/referrer");
-    createDirs(nixDBPath + "/failed");
-    Path profilesDir = nixStateDir + "/profiles";
-    createDirs(nixStateDir + "/profiles");
-    createDirs(nixStateDir + "/temproots");
-    Path gcRootsDir = nixStateDir + "/gcroots";
-    if (!pathExists(gcRootsDir)) {
-        createDirs(gcRootsDir);
-        if (symlink(profilesDir.c_str(), (gcRootsDir + "/profiles").c_str()) == -1)
-            throw SysError(format("creating symlink to `%1%'") % profilesDir);
-    }
-  
+    
    checkStoreNotSymlink();

    try {
@@ -76,7 +64,11 @@ LocalStore::LocalStore()
        printMsg(lvlError, "waiting for the big Nix store lock...");
        lockFile(globalLock, ltRead, true);
    }
-    
+
+    createDirs(nixDBPath + "/info");
+    createDirs(nixDBPath + "/referrer");
+    createDirs(nixDBPath + "/failed");
+
    int curSchema = getSchema();
    if (curSchema > nixSchemaVersion)
        throw Error(format("current Nix store schema is version %1%, but I only support %2%")
@@ -87,8 +79,6 @@ LocalStore::LocalStore()
    }
    if (curSchema == 1) throw Error("your Nix store is no longer supported");
    if (curSchema < nixSchemaVersion) upgradeStore12();
-
-    doFsync = queryBoolSetting("fsync-metadata", false);
 }


@@ -222,7 +212,7 @@ static Path tmpFileForAtomicUpdate(const Path & path)
 }


-void LocalStore::appendReferrer(const Path & from, const Path & to, bool lock)
+static void appendReferrer(const Path & from, const Path & to, bool lock)
 {
    Path referrersFile = referrersFileFor(from);
    
@@ -237,8 +227,6 @@ void LocalStore::appendReferrer(const Path & from, const Path & to, bool lock)
    
    string s = " " + to;
    writeFull(fd, (const unsigned char *) s.c_str(), s.size());
-
-    if (doFsync) fsync(fd);
 }


@@ -269,8 +257,6 @@ void LocalStore::rewriteReferrers(const Path & path, bool purge, PathSet referre
    
    writeFull(fd, (const unsigned char *) s.c_str(), s.size());

-    if (doFsync) fsync(fd);
-    
    fd.close(); /* for Windows; can't rename open file */

    if (rename(tmpFile.c_str(), referrersFile.c_str()) == -1)
@@ -351,7 +337,7 @@ void LocalStore::registerValidPath(const ValidPathInfo & info, bool ignoreValidi

    /* Atomically rewrite the info file. */
    Path tmpFile = tmpFileForAtomicUpdate(infoFile);
-    writeFile(tmpFile, s, doFsync);
+    writeFile(tmpFile, s);
    if (rename(tmpFile.c_str(), infoFile.c_str()) == -1)
        throw SysError(format("cannot rename `%1%' to `%2%'") % tmpFile % infoFile);

@@ -394,9 +380,6 @@ ValidPathInfo LocalStore::queryPathInfo(const Path & path, bool ignoreErrors)

    assertStorePath(path);

-    if (!isValidPath(path))
-        throw Error(format("path `%1%' is not valid") % path);
-
    std::map<Path, ValidPathInfo>::iterator lookup = pathInfoCache.find(path);
    if (lookup != pathInfoCache.end()) return lookup->second;
    
@@ -411,11 +394,7 @@ ValidPathInfo LocalStore::queryPathInfo(const Path & path, bool ignoreErrors)

    foreach (Strings::iterator, i, lines) {
        string::size_type p = i->find(':');
-        if (p == string::npos) {
-            if (!ignoreErrors)
-                throw Error(format("corrupt line in `%1%': %2%") % infoFile % *i);
-            continue; /* bad line */
-        }
+        if (p == string::npos) continue; /* bad line */
        string name(*i, 0, p);
        string value(*i, p + 2);
        if (name == "References") {
@@ -446,22 +425,7 @@ bool LocalStore::isValidPath(const Path & path)
    /* Files in the info directory starting with a `.' are temporary
       files. */
    if (baseNameOf(path).at(0) == '.') return false;
-
-    /* A path is valid if its info file exists and has a non-zero
-       size.  (The non-zero size restriction is to be robust to
-       certain kinds of filesystem corruption, particularly with
-       ext4.) */
-    Path infoFile = infoFileFor(path);
-
-    struct stat st;
-    if (lstat(infoFile.c_str(), &st)) {
-        if (errno == ENOENT) return false;
-        throw SysError(format("getting status of `%1%'") % infoFile);
-    }
-
-    if (st.st_size == 0) return false;
-    
-    return true;
+    return pathExists(infoFileFor(path));
 }


@@ -545,13 +509,6 @@ void LocalStore::startSubstituter(const Path & substituter, RunningSubstituter &

    case 0: /* child */
        try {
-            /* Hack to let "make check" succeed on Darwin.  The
-               libtool wrapper script sets DYLD_LIBRARY_PATH to our
-               libutil (among others), but Perl also depends on a
-               library named libutil.  As a result, substituters
-               written in Perl (i.e. all of them) fail. */
-            unsetenv("DYLD_LIBRARY_PATH");
-            
            fromPipe.readSide.close();
            toPipe.writeSide.close();
            if (dup2(toPipe.readSide, STDIN_FILENO) == -1)
@@ -741,7 +698,7 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
                StringSource source(dump);
                restorePath(dstPath, source);
            } else
-                writeFile(dstPath, dump);
+                writeStringToFile(dstPath, dump);

            canonicalisePathMetaData(dstPath);

@@ -796,7 +753,7 @@ Path LocalStore::addTextToStore(const string & name, const string & s,

            if (pathExists(dstPath)) deletePathWrapped(dstPath);

-            writeFile(dstPath, s);
+            writeStringToFile(dstPath, s);

            canonicalisePathMetaData(dstPath);
            
@@ -875,7 +832,7 @@ void LocalStore::exportPath(const Path & path, bool sign,
        Path tmpDir = createTempDir();
        AutoDelete delTmp(tmpDir);
        Path hashFile = tmpDir + "/hash";
-        writeFile(hashFile, printHash(hash));
+        writeStringToFile(hashFile, printHash(hash));

        Path secretKey = nixConfDir + "/signing-key.sec";
        checkSecrecy(secretKey);
@@ -951,7 +908,7 @@ Path LocalStore::importPath(bool requireSignature, Source & source)

        if (requireSignature) {
            Path sigFile = tmpDir + "/sig";
-            writeFile(sigFile, signature);
+            writeStringToFile(sigFile, signature);

            Strings args;
            args.push_back("rsautl");
@@ -1054,18 +1011,8 @@ void LocalStore::verifyStore(bool checkContents)
        } else if (!pathExists(*i)) {
            printMsg(lvlError, format("path `%1%' disappeared") % *i);
            invalidatePath(*i);
-        } else {
-            Path infoFile = infoFileFor(*i);
-            struct stat st;
-            if (lstat(infoFile.c_str(), &st))
-                throw SysError(format("getting status of `%1%'") % infoFile);
-            if (st.st_size == 0) {
-                printMsg(lvlError, format("removing corrupt info file `%1%'") % infoFile);
-                if (unlink(infoFile.c_str()) == -1)
-                    throw SysError(format("unlinking `%1%'") % infoFile);
-            }
-            else validPaths.insert(*i);
-        }
+        } else
+            validPaths.insert(*i);
    }


@@ -1169,16 +1116,4 @@ void LocalStore::verifyStore(bool checkContents)
 }


-/* Upgrade from schema 4 (Nix 0.11) to schema 5 (Nix >= 0.12).  The
-   old schema uses Berkeley DB, the new one stores store path
-   meta-information in files. */
-void LocalStore::upgradeStore12()
-{
-    throw Error(
-        "Your Nix store has a database in Berkeley DB format,\n"
-        "which is no longer supported. To convert to the new format,\n"
-        "please upgrade Nix to version 0.12 first.");
-}
-
-
 }
--- a/src/libstore/local-store.hh
+++ b/src/libstore/local-store.hh
@@ -158,17 +158,12 @@ private:
    /* Store paths for which the referrers file must be purged. */
    PathSet delayedUpdates;

-    /* Whether to do an fsync() after writing Nix metadata. */
-    bool doFsync;
-
    int getSchema();

    void registerValidPath(const ValidPathInfo & info, bool ignoreValidity = false);

    ValidPathInfo queryPathInfo(const Path & path, bool ignoreErrors = false);

-    void appendReferrer(const Path & from, const Path & to, bool lock);
-    
    void rewriteReferrers(const Path & path, bool purge, PathSet referrers);

    void flushDelayedUpdates();
@@ -179,20 +174,20 @@ private:
    
    void upgradeStore12();

-    struct GCState;
+    void gcPath(const GCOptions & options, GCResults & results,
+        const Path & path);
+
+    void gcPathRecursive(const GCOptions & options,
+        GCResults & results, PathSet & done, const Path & path);

-    bool tryToDelete(GCState & state, const Path & path);
-    
-    PathSet findDerivers(GCState & state, const Path & path);
-    
-    bool isActiveTempFile(const GCState & state,
-        const Path & path, const string & suffix);
-        
    void startSubstituter(const Path & substituter,
        RunningSubstituter & runningSubstituter);
 };


+/* Copy a path recursively. */
+void copyPath(const Path & src, const Path & dst);
+
 /* "Fix", or canonicalise, the meta-data of the files in a store path
   after it has been built.  In particular:
   - the last modification date on each file is set to 1 (i.e.,
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -2,6 +2,8 @@
 #include "store-api.hh"
 #include "local-store.hh"

+#include <aterm2.h>
+

 namespace nix {

@@ -10,12 +12,14 @@ Derivation derivationFromPath(const Path & drvPath)
 {
    assertStorePath(drvPath);
    store->ensurePath(drvPath);
-    return parseDerivation(readFile(drvPath));
+    ATerm t = ATreadFromNamedFile(drvPath.c_str());
+    if (!t) throw Error(format("cannot read aterm from `%1%'") % drvPath);
+    return parseDerivation(t);
 }


 void computeFSClosure(const Path & storePath,
-    PathSet & paths, bool flipDirection, bool includeOutputs)
+    PathSet & paths, bool flipDirection)
 {
    if (paths.find(storePath) != paths.end()) return;
    paths.insert(storePath);
@@ -26,15 +30,8 @@ void computeFSClosure(const Path & storePath,
    else
        store->queryReferences(storePath, references);

-    if (includeOutputs && isDerivation(storePath)) {
-        Derivation drv = derivationFromPath(storePath);
-        foreach (DerivationOutputs::iterator, i, drv.outputs)
-            if (store->isValidPath(i->second.path))
-                computeFSClosure(i->second.path, paths, flipDirection, true);
-    }
-
    foreach (PathSet::iterator, i, references)
-        computeFSClosure(*i, paths, flipDirection, includeOutputs);
+        computeFSClosure(*i, paths, flipDirection);
 }


--- a/src/libstore/misc.hh
+++ b/src/libstore/misc.hh
@@ -19,8 +19,7 @@ Derivation derivationFromPath(const Path & drvPath);
   `referrers' relation instead of the `references' relation is
   returned. */
 void computeFSClosure(const Path & storePath,
-    PathSet & paths, bool flipDirection = false,
-    bool includeOutputs = false);
+    PathSet & paths, bool flipDirection = false);

 /* Return the path corresponding to the output identifier `id' in the
   given derivation. */
--- a/src/libstore/optimise-store.cc
+++ b/src/libstore/optimise-store.cc
@@ -5,7 +5,6 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <errno.h>
-#include <stdio.h>


 namespace nix {
--- a/src/libstore/pathlocks.cc
+++ b/src/libstore/pathlocks.cc
@@ -8,6 +8,11 @@
 #include <sys/stat.h>
 #include <fcntl.h>

+#ifdef __CYGWIN__
+#include <windows.h>
+#include <sys/cygwin.h>
+#endif
+

 namespace nix {

@@ -16,24 +21,72 @@ int openLockFile(const Path & path, bool create)
 {
    AutoCloseFD fd;

+#ifdef __CYGWIN__
+    /* On Cygwin we have to open the lock file without "DELETE"
+       sharing mode; otherwise Windows will allow open lock files to
+       be deleted (which is almost but not quite what Unix does). */
+    char win32Path[MAX_PATH + 1];
+    cygwin_conv_to_full_win32_path(path.c_str(), win32Path);
+
+    SECURITY_ATTRIBUTES sa; /* required, otherwise inexplicably bad shit happens */
+    sa.nLength = sizeof sa;
+    sa.lpSecurityDescriptor = 0;
+    sa.bInheritHandle = TRUE;
+    HANDLE h = CreateFile(win32Path, GENERIC_READ | GENERIC_WRITE,
+        FILE_SHARE_READ | FILE_SHARE_WRITE, &sa, 
+        (create ? OPEN_ALWAYS : OPEN_EXISTING), 
+        FILE_ATTRIBUTE_NORMAL, 0);
+    if (h == INVALID_HANDLE_VALUE) {
+        if (create || GetLastError() != ERROR_FILE_NOT_FOUND)
+            throw Error(format("opening lock file `%1%'") % path);
+        fd = -1;
+    }
+    else
+        fd = cygwin_attach_handle_to_fd((char *) path.c_str(), -1, h, 1, O_RDWR);
+#else        
    fd = open(path.c_str(), O_RDWR | (create ? O_CREAT : 0), 0666);
    if (fd == -1 && (create || errno != ENOENT))
        throw SysError(format("opening lock file `%1%'") % path);
+#endif

    return fd.borrow();
 }


-void deleteLockFile(const Path & path, int fd)
+void deleteLockFilePreClose(const Path & path, int fd)
 {
+#ifndef __CYGWIN__
    /* Get rid of the lock file.  Have to be careful not to introduce
-       races.  Write a (meaningless) token to the file to indicate to
+       races. */
+    /* On Unix, write a (meaningless) token to the file to indicate to
       other processes waiting on this lock that the lock is stale
       (deleted). */
    unlink(path.c_str());
    writeFull(fd, (const unsigned char *) "d", 1);
    /* Note that the result of unlink() is ignored; removing the lock
       file is an optimisation, not a necessity. */
+#endif
+}
+
+
+void deleteLockFilePostClose(const Path & path)
+{
+#ifdef __CYGWIN__
+    /* On Windows, just try to delete the lock file.  This will fail
+       if anybody still has the file open.  We cannot use unlink()
+       here, because Cygwin emulates Unix semantics of allowing an
+       open file to be deleted (but fakes it - the file isn't actually
+       deleted until later, so a file with the same name cannot be
+       created in the meantime). */
+    char win32Path[MAX_PATH + 1];
+    cygwin_conv_to_full_win32_path(path.c_str(), win32Path);
+    if (DeleteFile(win32Path))
+        debug(format("delete of `%1%' succeeded") % path.c_str());
+    else
+        /* Not an error: probably means that the lock is still opened
+           by someone else. */
+        debug(format("delete of `%1%' failed: %2%") % path.c_str() % GetLastError());
+#endif
 }


@@ -167,13 +220,15 @@ PathLocks::~PathLocks()
 void PathLocks::unlock()
 {
    foreach (list<FDPair>::iterator, i, fds) {
-        if (deletePaths) deleteLockFile(i->second, i->first);
+        if (deletePaths) deleteLockFilePreClose(i->second, i->first);

        lockedPaths.erase(i->second);
        if (close(i->first) == -1)
            printMsg(lvlError,
                format("error (ignored): cannot close lock file on `%1%'") % i->second);

+	if (deletePaths) deleteLockFilePostClose(i->second);
+
        debug(format("lock released on `%1%'") % i->second);
    }

--- a/src/libstore/pathlocks.hh
+++ b/src/libstore/pathlocks.hh
@@ -12,8 +12,10 @@ namespace nix {
   because it doesn't exist.  Any other error throws an exception. */
 int openLockFile(const Path & path, bool create);

-/* Delete an open lock file. */
-void deleteLockFile(const Path & path, int fd);
+/* Delete an open lock file.  Both must be called to be fully portable
+   between Unix and Windows. */
+void deleteLockFilePreClose(const Path & path, int fd);
+void deleteLockFilePostClose(const Path & path);

 enum LockType { ltRead, ltWrite, ltNone };

--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -426,9 +426,8 @@ void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
    writeLongLong(options.maxFreed, to);
    writeInt(options.maxLinks, to);
    if (GET_PROTOCOL_MINOR(daemonVersion) >= 5) {
-        /* removed options */
-        writeInt(0, to);
-        writeInt(0, to);
+        writeInt(options.useAtime, to);
+        writeInt(options.maxAtime, to);
    }
    
    processStderr();
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1,7 +1,6 @@
 #include "store-api.hh"
 #include "globals.hh"
 #include "util.hh"
-#include "derivations.hh"

 #include <limits.h>

@@ -15,6 +14,8 @@ GCOptions::GCOptions()
    ignoreLiveness = false;
    maxFreed = 0;
    maxLinks = 0;
+    useAtime = false;
+    maxAtime = (time_t) -1;
 }


@@ -53,18 +54,6 @@ Path toStorePath(const Path & path)
 }


-string getNameOfStorePath(const Path & path)
-{
-    Path::size_type slash = path.rfind('/');
-    string p = slash == Path::npos ? path : string(path, slash + 1);
-    Path::size_type dash = p.find('-');
-    assert(dash != Path::npos);
-    string p2 = string(p, dash + 1);
-    if (isDerivation(p2)) p2 = string(p2, 0, p2.size() - 4);
-    return p2;
-}
-
-
 Path followLinksToStore(const Path & _path)
 {
    Path path = absPath(_path);
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -22,6 +22,10 @@ struct GCOptions
 {
    /* Garbage collector operation:

+       - `gcReturnRoots': find and return the set of roots for the
+         garbage collector.  These are the store paths symlinked to in
+         the `gcroots' directory.
+
       - `gcReturnLive': return the set of paths reachable from
         (i.e. in the closure of) the roots.

@@ -34,6 +38,7 @@ struct GCOptions
          `pathsToDelete', insofar as they are not reachable.
    */
    typedef enum {
+        gcReturnRoots,
        gcReturnLive,
        gcReturnDead,
        gcDeleteDead,
@@ -59,6 +64,22 @@ struct GCOptions
       has dropped below `maxLinks'. */
    unsigned int maxLinks;

+    /* Delete paths in order of ascending last access time.  I.e.,
+       prefer deleting unrecently used paths.  Useful in conjunction
+       with `maxFreed' and `maxLinks' (or manual interruption).  The
+       access time of a path is defined as the highest atime of any
+       non-directory, non-symlink file under that path.  Directories
+       and symlinks are ignored because their atimes are frequently
+       mass-updated, e.g. by `locate'.  Note that optimiseStore()
+       somewhat reduces the usefulness of this option: it hard-links
+       regular files and symlink together, giving them a "shared"
+       atime. */
+    bool useAtime;
+
+    /* Do not delete paths newer than `maxAtime'.  -1 means no age
+       limit. */
+    time_t maxAtime;
+
    GCOptions();
 };

@@ -243,12 +264,6 @@ void checkStoreName(const string & name);
 Path toStorePath(const Path & path);


-/* Get the "name" part of a store path, that is, the part after the
-   hash and the dash, and with any ".drv" suffix removed
-   (e.g. /nix/store/<hash>-foo-1.2.3.drv => foo-1.2.3). */
-string getNameOfStorePath(const Path & path);
-
-
 /* Follow symlinks until we end up with a path in the Nix store. */
 Path followLinksToStore(const Path & path);

--- a/src/libstore/upgrade-schema.cc
+++ b/src/libstore/upgrade-schema.cc
@@ -0,0 +1,108 @@
+#include "db.hh"
+#include "hash.hh"
+#include "util.hh"
+#include "local-store.hh"
+#include "globals.hh"
+#include "pathlocks.hh"
+#include "config.h"
+
+#include <iostream>
+
+
+namespace nix {
+
+
+Hash parseHashField(const Path & path, const string & s);
+
+
+/* Upgrade from schema 4 (Nix 0.11) to schema 5 (Nix >= 0.12).  The
+   old schema uses Berkeley DB, the new one stores store path
+   meta-information in files. */
+void LocalStore::upgradeStore12()
+{
+#if OLD_DB_COMPAT
+    
+#ifdef __CYGWIN__
+    /* Cygwin can't upgrade a read lock to a write lock... */
+    lockFile(globalLock, ltNone, true);
+#endif
+
+    if (!lockFile(globalLock, ltWrite, false)) {
+        printMsg(lvlError, "waiting for exclusive access to the Nix store...");
+        lockFile(globalLock, ltWrite, true);
+    }
+
+    printMsg(lvlError, "upgrading Nix store to new schema (this may take a while)...");
+
+    if (getSchema() >= nixSchemaVersion) return; /* somebody else beat us to it */
+
+    /* Open the old Nix database and tables. */
+    Database nixDB;
+    nixDB.open(nixDBPath);
+    
+    /* dbValidPaths :: Path -> ()
+
+       The existence of a key $p$ indicates that path $p$ is valid
+       (that is, produced by a succesful build). */
+    TableId dbValidPaths = nixDB.openTable("validpaths");
+
+    /* dbReferences :: Path -> [Path]
+
+       This table lists the outgoing file system references for each
+       output path that has been built by a Nix derivation.  These are
+       found by scanning the path for the hash components of input
+       paths. */
+    TableId dbReferences = nixDB.openTable("references");
+
+    /* dbReferrers :: Path -> Path
+
+       This table is just the reverse mapping of dbReferences.  This
+       table can have duplicate keys, each corresponding value
+       denoting a single referrer. */
+    // Not needed for conversion: it's just the inverse of
+    // references.
+    // TableId dbReferrers = nixDB.openTable("referrers");
+
+    /* dbDerivers :: Path -> [Path]
+
+       This table lists the derivation used to build a path.  There
+       can only be multiple such paths for fixed-output derivations
+       (i.e., derivations specifying an expected hash). */
+    TableId dbDerivers = nixDB.openTable("derivers");
+
+    Paths paths;
+    nixDB.enumTable(noTxn, dbValidPaths, paths);
+    
+    foreach (Paths::iterator, i, paths) {
+        ValidPathInfo info;
+        info.path = *i;
+        
+        Paths references;
+        nixDB.queryStrings(noTxn, dbReferences, *i, references);
+        info.references.insert(references.begin(), references.end());
+        
+        string s;
+        nixDB.queryString(noTxn, dbValidPaths, *i, s);
+        info.hash = parseHashField(*i, s);
+        
+        nixDB.queryString(noTxn, dbDerivers, *i, info.deriver);
+        
+        registerValidPath(info, true);
+        std::cerr << ".";
+    }
+
+    std::cerr << std::endl;
+
+    writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
+
+    lockFile(globalLock, ltRead, true);
+
+#else
+    throw Error(
+        "Your Nix store has a database in Berkeley DB format. To convert\n"
+        "to the new format, please compile Nix with Berkeley DB support.");
+#endif
+}
+
+
+}
--- a/src/libutil/Makefile.am
+++ b/src/libutil/Makefile.am
@@ -1,16 +1,16 @@
 pkglib_LTLIBRARIES = libutil.la

 libutil_la_SOURCES = util.cc hash.cc serialise.cc \
-  archive.cc xml-writer.cc
+  archive.cc aterm.cc aterm-map.cc xml-writer.cc

 libutil_la_LIBADD = ../boost/format/libformat.la

 pkginclude_HEADERS = util.hh hash.hh serialise.hh \
-  archive.hh xml-writer.hh types.hh
+  archive.hh aterm.hh aterm-map.hh xml-writer.hh types.hh

 if !HAVE_OPENSSL
 libutil_la_SOURCES += \
 md5.c md5.h sha1.c sha1.h sha256.c sha256.h md32_common.h
 endif

-AM_CXXFLAGS = -Wall -I$(srcdir)/..
+AM_CXXFLAGS = -Wall -I$(srcdir)/.. ${aterm_include}
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -1,5 +1,3 @@
-#include "config.h"
-
 #include <cerrno>
 #include <algorithm>
 #include <vector>
@@ -14,6 +12,8 @@
 #include "archive.hh"
 #include "util.hh"

+#include "config.h"
+

 namespace nix {

@@ -302,12 +302,7 @@ struct RestoreSink : ParseSink
 #if HAVE_POSIX_FALLOCATE
        if (len) {
            errno = posix_fallocate(fd, 0, len);
-            /* Note that EINVAL may indicate that the underlying
-               filesystem doesn't support preallocation (e.g. on
-               OpenSolaris).  Since preallocation is just an
-               optimisation, ignore it. */
-            if (errno && errno != EINVAL)
-                throw SysError(format("preallocating file of %1% bytes") % len);
+            if (errno) throw SysError(format("preallocating file of %1% bytes") % len);
        }
 #endif
    }
--- a/src/libutil/aterm-map.cc
+++ b/src/libutil/aterm-map.cc
@@ -0,0 +1,332 @@
+#include "aterm-map.hh"
+
+#include <iostream>
+
+#include <assert.h>
+#include <stdlib.h>
+
+#include <aterm2.h>
+
+
+namespace nix {
+
+
+static const unsigned int maxLoadFactor = /* 1 / */ 3;
+static unsigned int nrResizes = 0;
+static unsigned int sizeTotalAlloc = 0;
+static unsigned int sizeCurAlloc = 0;
+static unsigned int sizeMaxAlloc = 0;
+
+
+ATermMap::ATermMap(unsigned int expectedCount)
+{
+    init(expectedCount);
+}
+
+
+ATermMap::ATermMap(const ATermMap & map)
+{
+    init(map.maxCount);
+    copy(map.hashTable, map.capacity);
+}
+
+
+ATermMap & ATermMap::operator = (const ATermMap & map)
+{
+    if (this == &map) return *this;
+    free();
+    init(map.maxCount);
+    copy(map.hashTable, map.capacity);
+    return *this;
+}
+
+
+ATermMap::~ATermMap()
+{
+    free();
+}
+
+
+void ATermMap::init(unsigned int expectedCount)
+{
+    assert(sizeof(ATerm) * 2 == sizeof(KeyValue));
+    capacity = 0;
+    count = 0;
+    maxCount = 0;
+    hashTable = 0;
+    resizeTable(expectedCount);
+}
+
+
+void ATermMap::free()
+{
+    if (hashTable) {
+        ATunprotectArray((ATerm *) hashTable);
+        ::free(hashTable);
+        sizeCurAlloc -= sizeof(KeyValue) * capacity;
+        hashTable = 0;
+    }
+}
+
+
+static unsigned int roundToPowerOf2(unsigned int x)
+{
+    x--;
+    x |= x >> 1; x |= x >> 2; x |= x >> 4; x |= x >> 8; x |= x >> 16;
+    x++;
+    return x;
+}
+
+
+void ATermMap::resizeTable(unsigned int expectedCount)
+{
+    if (expectedCount == 0) expectedCount = 1;
+//     cout << maxCount << " -> " << expectedCount << endl;
+//     cout << maxCount << " " << size << endl;
+//     cout << (double) size / maxCount << endl;
+
+    unsigned int oldCapacity = capacity;
+    KeyValue * oldHashTable = hashTable;
+
+    maxCount = expectedCount;
+    capacity = roundToPowerOf2(maxCount * maxLoadFactor);
+    hashTable = (KeyValue *) calloc(sizeof(KeyValue), capacity);
+    sizeTotalAlloc += sizeof(KeyValue) * capacity;
+    sizeCurAlloc += sizeof(KeyValue) * capacity;
+    if (sizeCurAlloc > sizeMaxAlloc) sizeMaxAlloc = sizeCurAlloc;
+    ATprotectArray((ATerm *) hashTable, capacity * 2);
+    
+//     cout << capacity << endl;
+
+    /* Re-hash the elements in the old table. */
+    if (oldCapacity != 0) {
+        count = 0;
+        copy(oldHashTable, oldCapacity);
+        ATunprotectArray((ATerm *) oldHashTable);
+        ::free(oldHashTable);
+        sizeCurAlloc -= sizeof(KeyValue) * oldCapacity;
+        nrResizes++;
+    }
+}
+
+
+void ATermMap::copy(KeyValue * elements, unsigned int capacity)
+{
+    for (unsigned int i = 0; i < capacity; ++i)
+        if (elements[i].value) /* i.e., non-empty, non-deleted element */
+            set(elements[i].key, elements[i].value);
+}
+
+
+/* !!! use a bigger shift for 64-bit platforms? */
+static const unsigned int shift = 16;
+static const unsigned long knuth = (unsigned long) (0.6180339887 * (1 << shift));
+
+
+unsigned long ATermMap::hash1(ATerm key) const
+{
+    /* Don't care about the least significant bits of the ATerm
+       pointer since they're always 0. */
+    unsigned long key2 = ((unsigned long) key) >> 2;
+
+    /* Approximately equal to:
+    double d = key2 * 0.6180339887;
+    unsigned int h = (int) (capacity * (d - floor(d)));
+    */
+ 
+    unsigned long h = (capacity * ((key2 * knuth) & ((1 << shift) - 1))) >> shift;
+
+    return h;
+}
+
+
+unsigned long ATermMap::hash2(ATerm key) const
+{
+    unsigned long key2 = ((unsigned long) key) >> 2;
+    /* Note: the result must be relatively prime to `capacity' (which
+       is a power of 2), so we make sure that the result is always
+       odd. */
+    unsigned long h = ((key2 * 134217689) & (capacity - 1)) | 1;
+    return h;
+}
+
+
+static unsigned int nrItemsSet = 0;
+static unsigned int nrSetProbes = 0;
+
+
+void ATermMap::set(ATerm key, ATerm value)
+{
+    if (count == maxCount) resizeTable(capacity * 2 / maxLoadFactor);
+    
+    nrItemsSet++;
+    for (unsigned int i = 0, h = hash1(key); i < capacity;
+         ++i, h = (h + hash2(key)) & (capacity - 1))
+    {
+        // assert(h < capacity);
+        nrSetProbes++;
+        /* Note: to see whether a slot is free, we check
+           hashTable[h].value, not hashTable[h].key, since we use
+           value == 0 to mark deleted slots. */
+        if (hashTable[h].value == 0 || hashTable[h].key == key) {
+            if (hashTable[h].value == 0) count++;
+            hashTable[h].key = key;
+            hashTable[h].value = value;
+            return;
+        }
+    }
+        
+    abort();
+}
+
+
+static unsigned int nrItemsGet = 0;
+static unsigned int nrGetProbes = 0;
+
+
+ATerm ATermMap::get(ATerm key) const
+{
+    nrItemsGet++;
+    for (unsigned int i = 0, h = hash1(key); i < capacity;
+         ++i, h = (h + hash2(key)) & (capacity - 1))
+    {
+        nrGetProbes++;
+        if (hashTable[h].key == 0) return 0;
+        if (hashTable[h].key == key) return hashTable[h].value;
+    }
+    return 0;
+}
+
+
+void ATermMap::remove(ATerm key)
+{
+    for (unsigned int i = 0, h = hash1(key); i < capacity;
+         ++i, h = (h + hash2(key)) & (capacity - 1))
+    {
+        if (hashTable[h].key == 0) return;
+        if (hashTable[h].key == key) {
+            if (hashTable[h].value != 0) {
+                hashTable[h].value = 0;
+                count--;
+            }
+            return;
+        }
+    }
+}
+
+
+unsigned int ATermMap::size() const
+{
+    return count; /* STL nomenclature */
+}
+
+
+void printATermMapStats()
+{
+    using std::cerr;
+    using std::endl;
+    
+    cerr << "RESIZES: " << nrResizes << " "
+         << sizeTotalAlloc << " "
+         << sizeCurAlloc << " "
+         << sizeMaxAlloc << endl;
+        
+    cerr << "SET: "
+         << nrItemsSet << " "
+         << nrSetProbes << " "
+         << (double) nrSetProbes / nrItemsSet << endl;
+
+    cerr << "GET: "
+         << nrItemsGet << " "
+         << nrGetProbes << " "
+         << (double) nrGetProbes / nrItemsGet << endl;
+}
+
+
+#if 0
+int main(int argc, char * * argv)
+{
+    ATerm bottomOfStack;
+    ATinit(argc, argv, &bottomOfStack);
+
+    /* Make test terms. */
+    int nrTestTerms = 100000;
+    ATerm testTerms[nrTestTerms];
+
+    for (int i = 0; i < nrTestTerms; ++i) {
+        char name[10];
+        sprintf(name, "%d", (int) random() % 37);
+
+        int arity = i == 0 ? 0 : (random() % 37);
+        ATerm kids[arity];
+        for (int j = 0; j < arity; ++j)
+            kids[j] = testTerms[random() % i];
+        
+        testTerms[i] = (ATerm) ATmakeApplArray(ATmakeAFun(name, arity, ATfalse), kids);
+//         ATwriteToSharedTextFile(testTerms[i], stdout);
+//         printf("\n");
+    }
+
+
+    cout << "testing...\n";
+
+    
+    #define someTerm() (testTerms[(int) random() % nrTestTerms])
+
+
+    for (int test = 0; test < 100000; ++test) {
+        //cerr << test << endl;
+        unsigned int n = 300;
+        ATermMap map(300);
+        ATerm keys[n], values[n];
+        for (unsigned int i = 0; i < n; ++i) {
+            keys[i] = someTerm();
+            values[i] = someTerm();
+            map.set(keys[i], values[i]);
+            //cerr << "INSERT: " << keys[i] << " " << values[i] << endl;
+        }
+
+        unsigned int size = map.size();
+        assert(size <= n);
+        values[n - 1] = 0;
+        map.remove(keys[n - 1]);
+        assert(map.size() == size - 1);
+
+        unsigned int checksum;
+        unsigned int count = 0;
+        for (ATermMap::const_iterator i = map.begin(); i != map.end(); ++i, ++count) {
+            assert(i->key);
+            assert(i->value);
+            checksum += (unsigned int) (*i).key;
+            checksum += (unsigned int) (*i).value;
+            // cout << (*i).key << " " << (*i).value << endl;
+        }
+        assert(count == size - 1);
+
+        for (unsigned int i = 0; i < n; ++i) {
+            for (unsigned int j = i + 1; j < n; ++j)
+                if (keys[i] == keys[j]) goto x;
+            if (map.get(keys[i]) != values[i]) {
+                cerr << "MISMATCH: " << keys[i] << " " << values[i] << " " << map.get(keys[i]) << " " << i << endl;
+                abort();
+            }
+            if (values[i] != 0) {
+                checksum -= (unsigned int) keys[i];
+                checksum -= (unsigned int) values[i];
+            }
+        x:  ;
+        }
+
+        assert(checksum == 0);
+        
+        for (unsigned int i = 0; i < 100; ++i)
+            map.get(someTerm());
+        
+    }
+
+    printATermMapStats();
+}
+#endif
+
+ 
+}
--- a/src/libutil/aterm-map.hh
+++ b/src/libutil/aterm-map.hh
@@ -0,0 +1,130 @@
+#ifndef __ATERM_MAP_H
+#define __ATERM_MAP_H
+
+typedef struct _ATerm * ATerm;
+
+#include <assert.h>
+
+
+namespace nix {
+
+
+class ATermMap
+{
+public:
+
+    struct KeyValue
+    {
+        ATerm key;
+        ATerm value;
+    };
+
+private:
+
+    /* Hash table for the map.  We use open addressing, i.e., all
+       key/value pairs are stored directly in the table, and there are
+       no pointers.  Collisions are resolved through probing. */
+    KeyValue * hashTable;
+
+    /* Current size of the hash table. */
+    unsigned int capacity;
+
+    /* Number of elements in the hash table. */
+    unsigned int count;
+
+    /* Maximum number of elements in the hash table.  If `count'
+       exceeds this number, the hash table is expanded. */
+    unsigned int maxCount;
+    
+public:
+
+    /* Create a map.  `expectedCount' is the number of elements the
+       map is expected to hold. */
+    ATermMap(unsigned int expectedCount = 16);
+    
+    ATermMap(const ATermMap & map);
+    
+    ~ATermMap();
+
+    ATermMap & operator = (const ATermMap & map);
+        
+    void set(ATerm key, ATerm value);
+
+    ATerm get(ATerm key) const;
+
+    ATerm operator [](ATerm key) const
+    {
+        return get(key);
+    }
+
+    void remove(ATerm key);
+
+    unsigned int size() const;
+
+    struct const_iterator
+    {
+        const ATermMap & map;
+        unsigned int pos;
+        const_iterator(const ATermMap & map, int pos) : map(map)
+        {
+            this->pos = pos;
+        }
+        bool operator !=(const const_iterator & i)
+        {
+            return pos != i.pos;
+        }
+        void operator ++()
+        {
+            if (pos == map.capacity) return;
+            do { ++pos; 
+            } while (pos < map.capacity && map.hashTable[pos].value == 0);
+        }
+        const KeyValue & operator *()
+        {
+            assert(pos < map.capacity);
+            return map.hashTable[pos];
+        }
+        const KeyValue * operator ->()
+        {
+            assert(pos < map.capacity);
+            return &map.hashTable[pos];
+        }
+    };
+
+    friend class ATermMap::const_iterator;
+    
+    const_iterator begin() const
+    {
+        unsigned int i = 0;
+        while (i < capacity && hashTable[i].value == 0) ++i;
+        return const_iterator(*this, i);
+    }
+    
+    const_iterator end() const
+    {
+        return const_iterator(*this, capacity);
+    }
+
+private:
+    
+    void init(unsigned int expectedCount);
+
+    void free();
+
+    void resizeTable(unsigned int expectedCount);
+
+    void copy(KeyValue * elements, unsigned int capacity);
+    
+    inline unsigned long hash1(ATerm key) const;
+    inline unsigned long hash2(ATerm key) const;
+};
+
+
+/* Hack. */
+void printATermMapStats();
+
+ 
+}
+
+
+#endif /* !__ATERM_MAP_H */
--- a/src/libutil/aterm.cc
+++ b/src/libutil/aterm.cc
@@ -0,0 +1,55 @@
+#include "aterm.hh"
+
+#include <cstring>
+
+using std::string;
+
+
+string nix::atPrint(ATerm t)
+{
+    if (!t) throw Error("attempt to print null aterm");
+    char * s = ATwriteToString(t);
+    if (!s) throw Error("cannot print term");
+    return s;
+}
+
+
+std::ostream & operator << (std::ostream & stream, ATerm e)
+{
+    return stream << nix::atPrint(e);
+}
+
+
+nix::Error nix::badTerm(const format & f, ATerm t)
+{
+    char * s = ATwriteToString(t);
+    if (!s) throw Error("cannot print term");
+    if (strlen(s) > 1000) {
+        int len;
+        s = ATwriteToSharedString(t, &len);
+        if (!s) throw Error("cannot print term");
+    }
+    return Error(format("%1%, in `%2%'") % f.str() % (string) s);
+}
+
+
+ATerm nix::toATerm(const char * s)
+{
+    return (ATerm) ATmakeAppl0(ATmakeAFun((char *) s, 0, ATtrue));
+}
+
+
+ATerm nix::toATerm(const string & s)
+{
+    return toATerm(s.c_str());
+}
+
+
+ATermList nix::toATermList(const StringSet & ss)
+{
+    ATermList l = ATempty;
+    for (StringSet::const_reverse_iterator i = ss.rbegin();
+         i != ss.rend(); ++i)
+        l = ATinsert(l, toATerm(*i));
+    return l;
+}
--- a/src/libutil/aterm.hh
+++ b/src/libutil/aterm.hh
@@ -0,0 +1,55 @@
+#ifndef __ATERM_H
+#define __ATERM_H
+
+#include <aterm2.h>
+
+#include "types.hh"
+
+
+namespace nix {
+
+
+/* Print an ATerm. */
+string atPrint(ATerm t);
+
+class ATermIterator
+{
+    ATermList t;
+
+public:
+    ATermIterator(ATermList _t) : t(_t) { }
+    ATermIterator & operator ++ ()
+    {
+        t = ATgetNext(t);
+        return *this;
+    }
+    ATerm operator * ()
+    {
+        return ATgetFirst(t);
+    }
+    operator bool ()
+    {
+        return t != ATempty;
+    }
+};
+
+
+/* Throw an exception with an error message containing the given
+   aterm. */
+Error badTerm(const format & f, ATerm t);
+
+
+/* Convert strings to ATerms. */
+ATerm toATerm(const char * s);
+ATerm toATerm(const string & s);
+
+ATermList toATermList(const StringSet & ss);
+ 
+}
+
+
+/* Write an ATerm to an output stream. */
+std::ostream & operator << (std::ostream & stream, ATerm e);
+
+
+#endif /* !__ATERM_H */
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -1,9 +1,9 @@
 #include "serialise.hh"
 #include "util.hh"
+#include "aterm.hh"

 #include <cstring>

-
 namespace nix {


@@ -73,6 +73,67 @@ void writeStringSet(const StringSet & ss, Sink & sink)
 }


+void writeATerm(ATerm t, Sink & sink)
+{
+    int len;
+    unsigned char *buf = (unsigned char *) ATwriteToBinaryString(t, &len);
+    AutoDeleteArray<unsigned char> d(buf);
+    writeInt(len, sink);
+    sink(buf, len);
+}
+
+
+/* convert the ATermMap to a list of couple because many terms are shared
+   between the keys and between the values.  Thus the BAF stored by
+   writeATerm consume less memory space.  The list of couples is saved
+   inside a tree structure of /treedepth/ height because the serialiasation
+   of ATerm cause a tail recurssion on list tails. */
+void writeATermMap(const ATermMap & tm, Sink & sink)
+{
+    const unsigned int treedepth = 5;
+    const unsigned int maxarity = 128; // 2 < maxarity < MAX_ARITY (= 255)
+    const unsigned int bufsize = treedepth * maxarity;
+
+    AFun map = ATmakeAFun("map", 2, ATfalse);
+    AFun node = ATmakeAFun("node", maxarity, ATfalse);
+    ATerm empty = (ATerm) ATmakeAppl0(ATmakeAFun("empty", 0, ATfalse));
+
+    unsigned int c[treedepth];
+    ATerm *buf = new ATerm[bufsize];
+    AutoDeleteArray<ATerm> d(buf);
+
+    memset(buf, 0, bufsize * sizeof(ATerm));
+    ATprotectArray(buf, bufsize);
+
+    for (unsigned int j = 0; j < treedepth; j++)
+        c[j] = 0;
+
+    for (ATermMap::const_iterator i = tm.begin(); i != tm.end(); ++i) {
+         unsigned int depth = treedepth - 1;
+         ATerm term = (ATerm) ATmakeAppl2(map, i->key, i->value);
+         buf[depth * maxarity + c[depth]++] = term;
+         while (c[depth] % maxarity == 0) {
+             c[depth] = 0;
+             term = (ATerm) ATmakeApplArray(node, &buf[depth * maxarity]);
+             depth--;
+             buf[depth * maxarity + c[depth]++] = term;
+         }
+    }
+
+    unsigned int depth = treedepth;
+    ATerm last_node = empty;
+    while (depth--) {
+        buf[depth * maxarity + c[depth]++] = last_node;
+        while (c[depth] % maxarity)
+            buf[depth * maxarity + c[depth]++] = empty;
+        last_node = (ATerm) ATmakeApplArray(node, &buf[depth * maxarity]);
+    }
+
+    writeATerm(last_node, sink);
+    ATunprotectArray(buf);
+}
+
+
 void readPadding(unsigned int len, Source & source)
 {
    if (len % 8) {
@@ -136,4 +197,48 @@ StringSet readStringSet(Source & source)
 }


+ATerm readATerm(Source & source)
+{
+    unsigned int len = readInt(source);
+    unsigned char * buf = new unsigned char[len];
+    AutoDeleteArray<unsigned char> d(buf);
+    source(buf, len);
+    ATerm t = ATreadFromBinaryString((char *) buf, len);
+    if (t == 0)
+        throw SerialisationError("cannot read a valid ATerm.");
+    return t;
+}
+
+
+static void recursiveInitATermMap(ATermMap &tm, bool &stop, ATermAppl node)
+{
+    const unsigned int arity = ATgetArity(ATgetAFun(node));
+    ATerm key, value;
+
+    switch (arity) {
+        case 0:
+            stop = true;
+            return;
+        case 2:
+            key = ATgetArgument(node, 0);
+            value = ATgetArgument(node, 1);
+            tm.set(key, value);
+            return;
+        default:
+            for (unsigned int i = 0; i < arity && !stop; i++)
+              recursiveInitATermMap(tm, stop, (ATermAppl) ATgetArgument(node, i));
+            return;
+    }
+}
+
+ATermMap readATermMap(Source & source)
+{
+    ATermMap tm;
+    bool stop = false;
+
+    recursiveInitATermMap(tm, stop, (ATermAppl) readATerm(source));
+    return tm;
+}
+
+
 }
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -2,7 +2,7 @@
 #define __SERIALISE_H

 #include "types.hh"
-
+#include "aterm-map.hh"

 namespace nix {

@@ -98,12 +98,16 @@ void writeInt(unsigned int n, Sink & sink);
 void writeLongLong(unsigned long long n, Sink & sink);
 void writeString(const string & s, Sink & sink);
 void writeStringSet(const StringSet & ss, Sink & sink);
+void writeATerm(ATerm t, Sink & sink);
+void writeATermMap(const ATermMap & tm, Sink & sink);

 void readPadding(unsigned int len, Source & source);
 unsigned int readInt(Source & source);
 unsigned long long readLongLong(Source & source);
 string readString(Source & source);
 StringSet readStringSet(Source & source);
+ATerm readATerm(Source & source);
+ATermMap readATermMap(Source & source);


 MakeError(SerialisationError, Error)
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1,5 +1,9 @@
 #include "config.h"

+#ifdef __CYGWIN__
+#include <windows.h>
+#endif
+
 #include <iostream>
 #include <cerrno>
 #include <cstdio>
@@ -11,7 +15,6 @@
 #include <sys/wait.h>
 #include <sys/types.h>
 #include <fcntl.h>
-#include <unistd.h>

 #include "util.hh"

@@ -53,20 +56,10 @@ Path absPath(Path path, Path dir)
 {
    if (path[0] != '/') {
        if (dir == "") {
-#ifdef __GNU__
-            /* GNU (aka. GNU/Hurd) doesn't have any limitation on path
-               lengths and doesn't define `PATH_MAX'.  */
-            char *buf = getcwd(NULL, 0);
-            if (buf == NULL)
-#else
            char buf[PATH_MAX];
            if (!getcwd(buf, sizeof(buf)))
-#endif
                throw SysError("cannot get cwd");
            dir = buf;
-#ifdef __GNU__
-            free(buf);
-#endif
        }
        path = dir + "/" + path;
    }
@@ -227,13 +220,12 @@ string readFile(const Path & path)
 }


-void writeFile(const Path & path, const string & s, bool doFsync)
+void writeFile(const Path & path, const string & s)
 {
    AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
    if (fd == -1)
        throw SysError(format("opening file `%1%'") % path);
    writeFull(fd, (unsigned char *) s.c_str(), s.size());
-    if (doFsync) fsync(fd);
 }


@@ -305,10 +297,8 @@ static void _deletePath(const Path & path, unsigned long long & bytesFreed,
    if (lstat(path.c_str(), &st))
 	throw SysError(format("getting attributes of path `%1%'") % path);

-    if (!S_ISDIR(st.st_mode) && st.st_nlink == 1) {
-        bytesFreed += st.st_size;
-        blocksFreed += st.st_blocks;
-    }
+    bytesFreed += st.st_size;
+    blocksFreed += st.st_blocks;

    if (S_ISDIR(st.st_mode)) {
 	Strings names = readDirectory(path);
@@ -421,6 +411,16 @@ Paths createDirs(const Path & path)
 }


+void writeStringToFile(const Path & path, const string & s)
+{
+    AutoCloseFD fd(open(path.c_str(),
+        O_CREAT | O_EXCL | O_WRONLY, 0666));
+    if (fd == -1)
+        throw SysError(format("creating file `%1%'") % path);
+    writeFull(fd, (unsigned char *) s.c_str(), s.size());
+}
+
+
 LogType logType = ltPretty;
 Verbosity verbosity = lvlInfo;

@@ -810,8 +810,7 @@ void killUser(uid_t uid)
    case 0:
        try { /* child */

-            if (setuid(uid) == -1)
-                throw SysError("setting uid");
+            if (setuid(uid) == -1) abort();

 	    while (true) {
 		if (kill(-1, SIGKILL) == 0) break;
@@ -821,7 +820,7 @@ void killUser(uid_t uid)
 	    }

        } catch (std::exception & e) {
-            std::cerr << format("killing processes belonging to uid `%1%': %2%")
+            std::cerr << format("killing processes beloging to uid `%1%': %1%")
                % uid % e.what() << std::endl;
            quickExit(1);
        }
@@ -829,9 +828,8 @@ void killUser(uid_t uid)
    }
    
    /* parent */
-    int status = pid.wait(true);
-    if (status != 0)
-        throw Error(format("cannot kill processes for uid `%1%': %2%") % uid % statusToString(status));
+    if (pid.wait(true) != 0)
+        throw Error(format("cannot kill processes for uid `%1%'") % uid);

    /* !!! We should really do some check to make sure that there are
       no processes left running under `uid', but there is no portable
@@ -913,7 +911,15 @@ void closeMostFDs(const set<int> & exceptions)

 void quickExit(int status)
 {
+#ifdef __CYGWIN__
+    /* Hack for Cygwin: _exit() doesn't seem to work quite right,
+       since some Berkeley DB code appears to be called when a child
+       exits through _exit() (e.g., because execve() failed).  So call
+       the Windows API directly. */
+    ExitProcess(status);
+#else
    _exit(status);
+#endif
 }


@@ -951,6 +957,53 @@ void _interrupted()
 //////////////////////////////////////////////////////////////////////


+string packStrings(const Strings & strings)
+{
+    string d;
+    for (Strings::const_iterator i = strings.begin();
+         i != strings.end(); ++i)
+    {
+        unsigned int len = i->size();
+        d += len & 0xff;
+        d += (len >> 8) & 0xff;
+        d += (len >> 16) & 0xff;
+        d += (len >> 24) & 0xff;
+        d += *i;
+    }
+    return d;
+}
+
+    
+Strings unpackStrings(const string & s)
+{
+    Strings strings;
+    
+    string::const_iterator i = s.begin();
+    
+    while (i != s.end()) {
+
+        if (i + 4 > s.end())
+            throw Error(format("short db entry: `%1%'") % s);
+        
+        unsigned int len;
+        len = (unsigned char) *i++;
+        len |= ((unsigned char) *i++) << 8;
+        len |= ((unsigned char) *i++) << 16;
+        len |= ((unsigned char) *i++) << 24;
+
+        if (len == 0xffffffff) return strings; /* explicit end-of-list */
+        
+        if (i + len > s.end())
+            throw Error(format("short db entry: `%1%'") % s);
+
+        strings.push_back(string(i, i + len));
+        i += len;
+    }
+    
+    return strings;
+}
+
+
 Strings tokenizeString(const string & s, const string & separators)
 {
    Strings result;
@@ -1000,53 +1053,28 @@ string int2String(int n)
 }


+bool string2Int(const string & s, int & n)
+{
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+
+bool string2Int(const string & s, long long & n)
+{
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+
 bool hasSuffix(const string & s, const string & suffix)
 {
    return s.size() >= suffix.size() && string(s, s.size() - suffix.size()) == suffix;
 }


-void expect(std::istream & str, const string & s)
-{
-    char s2[s.size()];
-    str.read(s2, s.size());
-    if (string(s2, s.size()) != s)
-        throw Error(format("expected string `%1%'") % s);
-}
-
-
-string parseString(std::istream & str)
-{
-    string res;
-    expect(str, "\"");
-    int c;
-    while ((c = str.get()) != '"')
-        if (c == '\\') {
-            c = str.get();
-            if (c == 'n') res += '\n';
-            else if (c == 'r') res += '\r';
-            else if (c == 't') res += '\t';
-            else res += c;
-        }
-        else res += c;
-    return res;
-}
-
-
-bool endOfList(std::istream & str)
-{
-    if (str.peek() == ',') {
-        str.get();
-        return false;
-    }
-    if (str.peek() == ']') {
-        str.get();
-        return true;
-    }
-    return false;
-}
-
-
 void ignoreException()
 {
    try {
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -8,14 +8,12 @@
 #include <unistd.h>
 #include <signal.h>

-#include <cstdio>
-

 namespace nix {


 #define foreach(it_type, it, collection)                                \
-    for (it_type it = (collection).begin(); it != (collection).end(); ++it)
+    for (it_type it = collection.begin(); it != collection.end(); ++it)


 /* Return an environment variable. */
@@ -60,7 +58,7 @@ string readFile(int fd);
 string readFile(const Path & path);

 /* Write a string to a file. */
-void writeFile(const Path & path, const string & s, bool doFsync = false);
+void writeFile(const Path & path, const string & s);

 /* Read a line from a file descriptor. */
 string readLine(int fd);
@@ -91,6 +89,10 @@ Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
   list of created directories, in order of creation. */
 Paths createDirs(const Path & path);

+/* Create a file and write the given text to it.  The file is written
+   in binary mode (i.e., no end-of-line conversions).  The path should
+   not already exist. */
+void writeStringToFile(const Path & path, const string & s);

 template<class T, class A>
 T singleton(const A & a)
@@ -276,6 +278,11 @@ void inline checkInterrupt()
 MakeError(Interrupted, BaseError)


+/* String packing / unpacking. */
+string packStrings(const Strings & strings);
+Strings unpackStrings(const string & s);
+
+
 /* String tokenizer. */
 Strings tokenizeString(const string & s, const string & separators = " \t\n\r");

@@ -288,37 +295,43 @@ bool statusOk(int status);


 /* Parse a string into an integer. */
-template<class N> bool string2Int(const string & s, N & n)
-{
-    std::istringstream str(s);
-    str >> n;
-    return str && str.get() == EOF;
-}
-
 string int2String(int n);
+bool string2Int(const string & s, int & n);
+bool string2Int(const string & s, long long & n);


 /* Return true iff `s' ends in `suffix'. */
 bool hasSuffix(const string & s, const string & suffix);


-/* Read string `s' from stream `str'. */
-void expect(std::istream & str, const string & s);
-
-
-/* Read a C-style string from stream `str'. */
-string parseString(std::istream & str);
-
-
-/* Utility function used to parse legacy ATerms. */
-bool endOfList(std::istream & str);
-
-
 /* Exception handling in destructors: print an error message, then
   ignore the exception. */
 void ignoreException();


+/* STL functions such as sort() pass a binary function object around
+   by value, so it gets cloned a lot.  This is bad if the function
+   object has state or is simply large.  This adapter wraps the
+   function object to simulate passing by reference. */
+template<class F>
+struct binary_function_ref_adapter
+{
+    F * p;
+
+    binary_function_ref_adapter(F * _p)
+    {
+        p = _p;
+    }
+    
+    typename F::result_type operator () (
+        const typename F::first_argument_type & x,
+        const typename F::second_argument_type & y)
+    {
+        return (*p)(x, y);
+    }
+};
+
+
 }


--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
Nicolas Pierron	6468f63994	Fix typo.	2009-07-08 09:44:22 +00:00
Nicolas Pierron	9416202465	Add a way to cache result for future evaluations.	2009-07-08 09:27:35 +00:00
Nicolas Pierron	4941ba3413	Add a session independent cache.	2009-07-08 09:26:15 +00:00
Nicolas Pierron	7244b9b861	Create a cache of reduce operations which are session independent.	2009-07-08 09:18:26 +00:00