anchor.diff:    src = fetchFromGitHub {
       owner = "jeffreytse";
       repo = "zsh-vi-mode";
  -    rev = "b612d16b0873917a034076793914ade9b4ef3635";
  -    sha256 = "tlAgsIHHZPnk6NznOdzvLHlB1J2FkwCuGLlGHzR06Jg=";
  +    rev = "v${version}";
  +    sha256 = "EOYqHh0rcgoi26eopm6FTl81ehak5kXMmzNcnJDH8/E=";
     };
   
     # This overrides the shell code that is run during the installPhase.
  
positive.code:     cp *.zsh $out/
    '';
  }
  
  
negative.code: # todo: contribute this back upstream to nixpkgs
  { stdenv, fetchFromGitHub }:
  
  stdenv.mkDerivation rec {
    name = "zsh-vi-mode";
    version = "0.8.5";
  
    # fetchFromGitHub is a build support function that fetches a GitHub
    # repository and extracts into a directory; so we can use it
  