anchor.diff:  
     postInstall = ''
       # Fix path to mlton libraries.
  -    substituteInPlace $(pwd)/install/usr/bin/mlton --replace '/usr/lib/mlton' $out/lib/mlton
  +    substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace '/${usr_prefix}/lib/mlton' $out/lib/mlton
   
       # Path to libgmp.
  -    substituteInPlace $(pwd)/install/usr/bin/mlton --replace "-link-opt '-lm -lgmp'" "-link-opt '-lm -lgmp -L${gmp}/lib'"
  +    substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace "-link-opt '-lm -lgmp'" "-link-opt '-lm -lgmp -L${gmp}/lib'"
   
       # Path to gmp.h.
  -    substituteInPlace $(pwd)/install/usr/bin/mlton --replace "-cc-opt '-O1 -fno-common'" "-cc-opt '-O1 -fno-common -I${gmp}/include'"
  +    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 $(pwd)/install/usr/bin/mlton --replace "gcc='gcc'" "gcc='"$(type -p gcc)"'"
  +    substituteInPlace $(pwd)/install/${usr_prefix}/bin/mlton --replace "gcc='gcc'" "gcc='"$(type -p gcc)"'"
   
       # Copy files to final positions.
  -    cp -r $(pwd)/install/usr/bin $out
  -    cp -r $(pwd)/install/usr/lib $out
  -    cp -r $(pwd)/install/usr/man $out
  +    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 = {
  
positive.code: 
  let
    version = "20130715";
  in
  stdenv.mkDerivation rec {
    name = "mlton-${version}";
  
negative.code:     substituteInPlace $(pwd)/Makefile --replace '/bin/cp' $(type -p cp)
  
      # Fix paths in the binary distribution.
      BIN_DIST_DIR="$(pwd)/../${usr_prefix}"
      for f in "bin/mlton" "lib/mlton/platform" "lib/mlton/static-library" ; do
        substituteInPlace "$BIN_DIST_DIR/$f" --replace '/${usr_prefix}/bin/env bash' $(type -p bash)
      done
  
      substituteInPlace $(pwd)/../${usr_prefix}/bin/mlton --replace '/${usr_prefix}/lib/mlton' $(pwd)/../${usr_prefix}/lib/mlton
    '';
  
    preBuild = ''
      # To build the source we have to put the binary distribution in the $PATH.
      export PATH="$PATH:$(pwd)/../${usr_prefix}/bin/"
  
      # Let the builder execute the binary distribution.
      chmod u+x $(pwd)/../${usr_prefix}/bin/mllex
      chmod u+x $(pwd)/../${usr_prefix}/bin/mlyacc
      chmod u+x $(pwd)/../${usr_prefix}/bin/mlton
  
      # So the builder runs the binary compiler with gmp.
      export LD_LIBRARY_PATH=${gmp}/lib:$LD_LIBRARY_PATH
  
    '' + stdenv.lib.optionalString stdenv.isLinux ''
      # Patch ELF interpreter.
      patchelf --set-interpreter ${stdenv.glibc}/lib/ld-linux-x86-64.so.2 $(pwd)/../${usr_prefix}/lib/mlton/mlton-compile
      for e in mllex mlyacc ; do
        patchelf --set-interpreter ${stdenv.glibc}/lib/ld-linux-x86-64.so.2 $(pwd)/../${usr_prefix}/bin/$e
      done
    '';
  
  