* Added plain lambdas, e.g., `let { id = x: x; const = x: y: x; }'.

`bla:' is now no longer parsed as a URL.

* Re-enabled support for the `args' attribute in derivations to
  specify command line arguments to the builder, e.g.,

    ...
    builder = /usr/bin/python;
    args = ["-c" ./builder.py];
    ...

src/libexpr/eval.cc

@@ -195,6 +195,7 @@ Expr evalExpr2(EvalState & state, Expr e)
          cons == "Int" ||
          cons == "Bool" ||
          cons == "Function" ||
+         cons == "Function1" ||
          cons == "Attrs" ||
          cons == "List"))
         return e;
@@ -226,6 +227,12 @@ Expr evalExpr2(EvalState & state, Expr e)
             return evalExpr(state, 
                 substArgs(e4, formals, evalExpr(state, e2)));
         
+        else if (atMatch(m, e1) >> "Function1" >> name >> e4) {
+            ATermMap subs;
+            subs.set(name, e2);
+            return evalExpr(state, substitute(subs, e4));
+        }
+        
         else throw badTerm("expecting a function or primop", e1);
     }