anchor.diff:  { minor_version, major_version, patch_version
  -, url ? null
  -, sha256, ...}@args:
  +, ...}@args:
   let
     versionNoPatch = "${toString major_version}.${toString minor_version}";
     version = "${versionNoPatch}.${toString patch_version}";
  -  real_url = if url == null then
  -    "http://caml.inria.fr/pub/distrib/ocaml-${versionNoPatch}/ocaml-${version}.tar.xz"
  -  else url;
     safeX11 = stdenv: !(stdenv.isAarch32 || stdenv.isMips);
   in
   
  
positive.code:   inherit name;
    inherit version;
  
    src = fetchurl {
      url = real_url;
      inherit sha256;
    };
  
    prefixKey = "-prefix ";
    configureFlags =
  
negative.code: assert aflSupport -> stdenv.lib.versionAtLeast version "4.05";
  assert flambdaSupport -> stdenv.lib.versionAtLeast version "4.03";
  assert spaceTimeSupport -> stdenv.lib.versionAtLeast version "4.04";
  
  let
    src = args.src or (fetchurl {
      url = args.url or "http://caml.inria.fr/pub/distrib/ocaml-${versionNoPatch}/ocaml-${version}.tar.xz";
      inherit (args) sha256;
    });
  in
  
  let
     useNativeCompilers = !stdenv.isMips;
  