anchor.diff:  
   stdenv.mkDerivation rec {
   
  +  x11env = buildEnv { name = "x11env"; paths = [libX11 xproto]; };
  +  x11lib = x11env + "/lib";
  +  x11inc = x11env + "/include";
  +
     name = "ocaml-4.01.0";
   
     src = fetchurl {
  
positive.code:   };
  
    prefixKey = "-prefix ";
    configureFlags = ["-no-tk"] ++ optionals useX11 [ "-x11lib" x11 ];
    buildFlags = "world" + optionalString useNativeCompilers " bootstrap world.opt";
    buildInputs = [ncurses] ++ optionals useX11 [ x11 ];
    installTargets = "install" + optionalString useNativeCompilers " installopt";
    preConfigure = ''
      CAT=$(type -tp cat)
  
negative.code: { stdenv, fetchurl, ncurses, buildEnv, libX11, xproto }:
  
  let
     useX11 = !stdenv.isArm && !stdenv.isMips;
  