anchor.diff:    ghc-parser-src       = filterSource cleanSource ./ghc-parser;
     ihaskell-display-src = filterSource cleanSource ./ihaskell-display;
   
  -  foundation-src = nixpkgs.fetchFromGitHub {
  -    owner = "haskell-foundation";
  -    repo = "foundation";
  -    rev = "c87c00c5988398f7fb6bbf8ebc79250fc3e9a363";
  -    sha256 = "122kddjxyykkvw58v6wvvmgyqng9383iy2awpa39hs6zw0cbh3bl";
  -  };
     profunctors-src = nixpkgs.fetchFromGitHub {
       owner = "ekmett";
       repo = "profunctors";
  
positive.code: 
        cryptohash-md5    = nixpkgs.haskell.lib.doJailbreak super.cryptohash-md5;
        cryptohash-sha1   = nixpkgs.haskell.lib.doJailbreak super.cryptohash-sha1;
        basement          = self.callCabal2nix "basement" (foundation-src + "/basement") {};
        foundation        = nixpkgs.haskell.lib.appendPatch super.foundation (nixpkgs.fetchpatch {
          url = "https://gitlab.haskell.org/ghc/head.hackage/-/raw/a89f0189a628e5de9a6e8fe9830e29a3e61e316c/patches/foundation-0.0.25.patch";
          sha256 = "0fhdqw01qqmzjn67d289m8gpb8wl1rwwc3hcjx92djxk493ialvj";
        });
        memory            = nixpkgs.haskell.lib.appendPatch super.memory (nixpkgs.fetchpatch {
          url = "https://gitlab.haskell.org/ghc/head.hackage/-/raw/c89c1e27af8f180b3be476e102147557f922b224/patches/memory-0.15.0.patch";
          sha256 = "0mkjbrzi05h1xds8rf5wfky176hrl03q0d7ipklp9x4ls3yyqj5x";
  
negative.code: let
    nixpkgs-src = builtins.fetchTarball {
      url = "https://github.com/NixOS/nixpkgs/tarball/8795d39ce70f04e3fd609422d522e5b2594f3a70";
      sha256 = "01w7q0nqydippj0ygbg77byb770snhc5rnqzc6isws58642l8z4s";
    };
  in
  { compiler ? "ghc901"
  