anchor.diff:      url = "https://github.com/crystal-lang/crystal/releases/download/${version}/crystal-${version}-1-${arch}.tar.gz";
       sha256 =
         {
  -        "x86_64-linux" = "03c1nmjibz8f7yhrczd49gmccx4ivqz121c64hl384w69227p7bq";
  -        "i686-linux" = "1s8gpmxa9wpcc2a9csl205lcpipn1i7gwybapby3q34y7xnq9160";
  -        "x86_64-darwin" = "1bnfxb0hbkx4qlkc1l88sdhcnhacqzy31hh7ksz0prah83g6vbxa";
  +        "x86_64-linux" = "0nhs7swbll8hrk15kmmywngkhij80x62axiskb1gjmiwvzhlh0qx";
  +        "i686-linux" = "03xp8d3lqflzzm26lpdn4yavj87qzgd6xyrqxp2pn9ybwrq8fx8a";
  +        "x86_64-darwin" = "1prz6c1gs8z7dgpdy2id2mjn1c8f5p2bf9b39985bav448njbyjz";
         }."${stdenv.system}" or (throw "system ${stdenv.system} not supported");
     };
   
     src = fetchurl {
       url = "https://github.com/crystal-lang/crystal/archive/${version}.tar.gz";
  -    sha256 = "0iw5i4hjzfxykwfdyzix23pgm3gxd79r9yss3abvva8cf7ci37sv";
  +    sha256 = "05ymwmjkl1b4m888p725kybpiap5ag2vj8l07d59j02inm5r0rcv";
     };
   
     # crystal on Darwin needs libiconv to build
     buildInputs = [
  -    boehmgc libatomic_ops pcre libevent llvm_39 makeWrapper
  +    boehmgc libatomic_ops pcre libevent llvm_4 makeWrapper
     ] ++ stdenv.lib.optionals stdenv.isDarwin [
       libiconv
     ];
  
positive.code:     install -Dm644 etc/completion.bash $out/share/bash-completion/completions/crystal
      install -Dm644 etc/completion.zsh $out/share/zsh/site-functions/_crystal
  
      install -Dm644 LICENSE $out/share/licenses/crystal/LICENSE
    '';
  
  
negative.code: { stdenv, fetchurl, boehmgc, libatomic_ops, pcre, libevent, libiconv, llvm_4, makeWrapper }:
  
  stdenv.mkDerivation rec {
    version = "0.23.0";
    name = "crystal-${version}-1";
    arch =
      {
  