anchor.diff:  , ocamlPackages ? pkgs.ocaml-ng.ocamlPackages_4_06
   , buildIde ? true
   , buildDoc ? true
  -, doCheck ? true
  +, doInstallCheck ? true
   }:
   
   with pkgs;
  
positive.code: 
    prefixKey = "-prefix ";
  
    buildFlags = [ "world" ] ++ optional buildDoc "doc-html";
  
    installTargets = [ "install" ] ++ optional buildDoc "install-doc-html";
  
    inherit doCheck;
  
  }
  
negative.code: 
  # nix-shell supports the --arg option (see Nix doc) that allows you for
  # instance to do this:
  # $ nix-shell --arg ocamlPackages "(import <nixpkgs> {}).ocaml-ng.ocamlPackages_4_05" --arg buildIde false
  
  # You can also compile Coq and "install" it by running:
  # $ make clean # (only needed if you have left-over compilation files)
  # $ nix-build
  # at the root of the Coq repository.
  # nix-build also supports the --arg option, so you will be able to do:
  # $ nix-build --arg doInstallCheck false
  # if you want to speed up things by not running the test-suite.
  # Once the build is finished, you will find, in the current directory,
  # a symlink to where Coq was installed.
  