anchor.diff:        declarativity of logic programming.
       '';
   
  -    license = "GPLv2+";
  -
       maintainers = [ stdenv.lib.maintainers.simons ];
       platforms = stdenv.lib.platforms.gnu;
     };
  
positive.code: { stdenv, fetchurl }:
  
  stdenv.mkDerivation rec {
    name = "gprolog-1.4.0";
  
    src = fetchurl {
      urls = [
        "mirror://gnu/gprolog/${name}.tar.gz"
        "http://www.gprolog.org/${name}.tar.gz"
      ];
      sha256 = "1l66k66ryfw1nfi2wlvsyq4cmr6mm95f4iay1fxdk3hdk3fjyjl0";
    };
  
    configurePhase = "cd src ;"
  
negative.code:     + "--with-examples-dir=$out/share/doc/${name}/examples "
      + "--with-doc-dir=$out/share/doc/${name}";
  
    postInstall = ''
      ln -vs "$out/share/${name}/include" "$out/include"
      ln -vs "$out/share/${name}/lib" "$out/lib"
    '';
  
    doCheck = true;
    enableParallelBuilding = true;
  
    meta = {
      homepage = "http://www.gnu.org/software/gprolog/";
      description = "GNU Prolog, a free Prolog compiler with constraint solving over finite domains";
      license = "GPLv2+";
  
      longDescription = ''
        GNU Prolog is a free Prolog compiler with constraint solving
  