old generations of *all* profiles in /nix/var/nix/profiles, then
  runs the garbage collector.  Quick way to get rid of all old stuff.
  Of course, one cannot roll back to earlier points in time after
  this.

* Install libexpr header files.

  marshalling code.

* Optimise header file usage a bit.
* Compile the parser as C++.

  and returns its path.  This can be used to (for instance) write
  builders inside a Nix expression, e.g.,

  stdenv.mkDerivation {
    builder = "
      source $stdenv/setup
      ...
    ";
    ...
  }

  bad flex doesn't have lexical restrictions, the current solution
  isn't quite right...)

  evaluate its arguments.

  a warning.

  derivation attributes to flatten them into strings.  This is
  possible since string can nowadays be wrapped in contexts that
  describe the derivations/sources referenced by the evaluation of the
  string.

  "powerpc-linux".

  location when building RPMs (fixes NIX-58).

  normalised away.

  an XML representation stored in a string.  This should be useful to
  pass structured information to builders.

  $ nix-env -qa --system-filter \* --arg system '"powerpc-darwin"'

  to override the system from the default value (__currentSystem in
  all-packages.nix).

  foo.nix -A attr --arg name value" will work if (name, value) is
  needed in the evaluation leading up to "attr".

  all the primops.  This allows Nix expressions to test for new
  primops and take appropriate action if they're not available.  For
  instance, rather than calling a primop `foo' directly, they could
  say `if builtins ? foo then builtins.foo ... else ...'.