anchor.diff:  
     installPhase = ''
       mkdir -p $out/{bin,share/man/man1,share/bash-completion/completions}
  +    substituteInPlace memo \
  +      --replace "ack "  "${ag}/bin/ag " \
  +      --replace "tree " "${tree}/bin/tree "
       mv memo $out/bin/
       mv doc/memo.1 $out/share/man/man1/memo.1
       mv completion/memo.bash $out/share/bash-completion/completions/memo.sh
  
positive.code: { fetchFromGitHub, ack , tree, stdenv, ... }:
  
  stdenv.mkDerivation rec {
  
  
negative.code:     maintainers = [ stdenv.lib.maintainers.mrVanDalo ];
      platforms = stdenv.lib.platforms.all;
    };
  }
  