anchor.diff:      else if stdenv.system == "x86_64-linux" then (fetchurl {
           url = "http://sourceforge.net/projects/mlton/files/mlton/${version}/${name}-1.amd64-linux.tgz";
           sha256 = "0fyhwxb4nmpirjbjcvk9f6w67gmn2gkz7xcgz0xbfih9kc015ygn";
  +    })
  +    else if stdenv.system == "x86_64-darwin" then (fetchurl {
  +        url = "http://sourceforge.net/projects/mlton/files/mlton/${version}/${name}-1.amd64-darwin.gmp-macports.tgz";
  +        sha256 = "044wnh9hhg6if886xy805683k0as347xd37r0r1yi4x7qlxzzgx9";
       })
       else throw "Architecture not supported";
   
  
positive.code: 
      homepage = http://mlton.org/;
      license = "bsd";
      platforms = [ "i686-linux" "x86_64-linux" ];
    };
  }
  
negative.code: 
    postInstall = ''
      # Fix path to mlton libraries.
      substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace '/${usr_prefix}/lib/mlton' $out/lib/mlton
  
      # Path to libgmp.
      substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace "-link-opt '-lm -lgmp'" "-link-opt '-lm -lgmp -L${gmp}/lib'"
  
      # Path to gmp.h.
      substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace "-cc-opt '-O1 -fno-common'" "-cc-opt '-O1 -fno-common -I${gmp}/include'"
  
      # Path to the same gcc used in the build; needed at runtime.
      substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace "gcc='gcc'" "gcc='"$(type -p gcc)"'"
  
      # Copy files to final positions.
      cp -r $(pwd)/install/${usr_prefix}/bin $out
      cp -r $(pwd)/install/${usr_prefix}/lib $out
      cp -r $(pwd)/install/${usr_prefix}/man $out
    '';
  
    meta = {
  