anchor.diff:  { stdenv, fetchurl, boehmgc, libatomic_ops, pcre, libevent, libiconv, llvm_4, makeWrapper }:
   
   stdenv.mkDerivation rec {
  -  version = "0.23.0";
  -  name = "crystal-${version}-1";
  +  version = "0.23.1";
  +  patch = "3";
  +  name = "crystal-${version}-${patch}";
     arch =
       {
         "x86_64-linux" = "linux-x86_64";
  
positive.code:     }."${stdenv.system}" or (throw "system ${stdenv.system} not supported");
  
    prebuiltBinary = fetchurl {
      url = "https://github.com/crystal-lang/crystal/releases/download/${version}/crystal-${version}-1-${arch}.tar.gz";
      sha256 =
        {
          "x86_64-linux" = "0nhs7swbll8hrk15kmmywngkhij80x62axiskb1gjmiwvzhlh0qx";
          "i686-linux" = "03xp8d3lqflzzm26lpdn4yavj87qzgd6xyrqxp2pn9ybwrq8fx8a";
          "x86_64-darwin" = "1prz6c1gs8z7dgpdy2id2mjn1c8f5p2bf9b39985bav448njbyjz";
        }."${stdenv.system}" or (throw "system ${stdenv.system} not supported");
    };
  
    src = fetchurl {
      url = "https://github.com/crystal-lang/crystal/archive/${version}.tar.gz";
      sha256 = "05ymwmjkl1b4m888p725kybpiap5ag2vj8l07d59j02inm5r0rcv";
    };
  
    # crystal on Darwin needs libiconv to build
  
negative.code:   sourceRoot = ".";
  
    fixPrebuiltBinary = if stdenv.isDarwin then ''
      wrapProgram $(pwd)/crystal-${version}-${patch}/embedded/bin/crystal \
          --suffix DYLD_LIBRARY_PATH : $libPath
    ''
    else ''
      patchelf --set-interpreter $(cat $NIX_CC/nix-support/dynamic-linker) \
        crystal-${version}-${patch}/embedded/bin/crystal
      patchelf --set-rpath ${ stdenv.lib.makeLibraryPath [ stdenv.cc.cc ] } \
        crystal-${version}-${patch}/embedded/bin/crystal
    '';
  
    newline = "\n";
  
    buildPhase = ''
      # patch the script which launches the prebuilt compiler
      patchShebangs $(pwd)/crystal-${version}-${patch}/bin/crystal
      patchShebangs $(pwd)/crystal-${version}/bin/crystal
      # Due to https://github.com/crystal-lang/crystal/issues/4719,
      # when building Crystal with LLVM 4 with debug infos from prebuilt binary (w/ LLVM 3.8) will always be failed.
      # So we are going to build a LLVM 4 version without debug info,
      # and use it to build Crystal with debug info on LLVM 4.
      substituteInPlace $(pwd)/crystal-${version}/Makefile --replace \
        "release ?=" "no_debug ?= ##${newline}force_rebuild ?= ##${newline}release ?="
      substituteInPlace $(pwd)/crystal-${version}/Makefile --replace \
        "FLAGS := " "FLAGS := \$(if \$(no_debug),--no-debug )"
      substituteInPlace $(pwd)/crystal-${version}/Makefile --replace \
        "$(O)/crystal:" "\$(O)/crystal: \$(if \$(force_rebuild),../rebuild.tmp)"
      ${fixPrebuiltBinary}
  
      cd crystal-${version}
      # Build without debug infos on LLVM 4
      make release=1 no_debug=1 PATH="../crystal-${version}-${patch}/bin:$PATH"
      
      # Rebuild Crystal with debug infos from the binary we just built
      touch $(pwd)/../rebuild.tmp
      wrapProgram .build/crystal \
          --suffix LIBRARY_PATH : $libPath
      make release=1 force_rebuild=1
      make doc
    '';
  
  