anchor.diff:  
     postInstall = lib.optionalString stdenv.hostPlatform.isDarwin ''
       mkdir $out/Applications
  -    mv $out/bin/${meta.mainProgram}.app $out/Applications/
  -    ln -s $out/{Applications/${meta.mainProgram}.app/Contents/MacOS,bin}/${meta.mainProgram}
  +    mv $out/bin/${pname}.app $out/Applications/
  +    ln -s $out/{Applications/${pname}.app/Contents/MacOS,bin}/${pname}
     '';
   
     meta = with lib; {
  
positive.code:     license = with licenses; [ gpl3Plus ];
      maintainers = with maintainers; [ OPNA2608 ];
      platforms = platforms.all;
      mainProgram = "mt32emu-qt";
    };
  }
  
negative.code: , withJack ? stdenv.hostPlatform.isUnix, libjack2
  }:
  
  let
    char2underscore = char: str: lib.replaceChars [ char ] [ "_" ] str;
  in
  mkDerivation rec {
    pname = "mt32emu-qt";
    version = "1.10.2";
  
    src = fetchFromGitHub {
      owner = "munt";
      repo = "munt";
      rev = "${char2underscore "-" pname}_${char2underscore "." version}";
      sha256 = "1dh5xpnsgx367ch45mm5c2p26vnxf3shax2afg2cd2lrbrlii7l9";
    };
  
    postPatch = ''
  