* `nix-env -qa --description' shows human-readable descriptions of

packages (provided that they have a `meta.description' attribute).
  E.g.,

  $ ./src/nix-env/nix-env -qa --description gcc
  gcc-4.0.2   GNU Compiler Collection, 4.0.x (cross-compiler for sparc-linux)
  gcc-4.0.2   GNU Compiler Collection, 4.0.x (cross-compiler for mips-linux)
  gcc-4.0.2   GNU Compiler Collection, 4.0.x (cross-compiler for arm-linux)
  gcc-4.0.2   GNU Compiler Collection, 4.0.x

src/libexpr/eval.hh

@@ -56,6 +56,7 @@ Expr evalFile(EvalState & state, const Path & path);
 string evalString(EvalState & state, Expr e);
 Path evalPath(EvalState & state, Expr e);
 ATermList evalList(EvalState & state, Expr e);
+ATerm coerceToString(Expr e);
 
 /* Print statistics. */
 void printEvalStats(EvalState & state);