anchor.diff:    src = fetchgit {
       url = "git://git.haskell.org/ghc.git";
       inherit rev;
  -    sha256 = "1h064nikx5srsd7qvz19f6dxvnpfjp0b3b94xs1f4nar18hzf4j0";
  +    sha256 = "08vj9ca7rq7rv8pjfl14fg2lg9d6zisrwlq6bi5vzr006816dy8y";
     };
   
     postPatch = "patchShebangs .";
  
positive.code:   # If enabled GHC will be build with the GPL-free but slower integer-simple
    # library instead of the faster but GPLed integer-gmp library.
  , enableIntegerSimple ? false, gmp
  , version ? "8.1.20170106"
  }:
  
  let
  
negative.code: 
    commonBuildInputs = [ ghc perl autoconf automake happy alex python3 ];
  
    rev = "14457cf6a50f708eecece8f286f08687791d51f7";
  
    commonPreConfigure =  ''
      echo ${version} >VERSION
  