anchor.diff:      for i in $out/bin/*; do
         wrapProgram $i \
           --prefix PATH : "${tcl}/bin" \
  -        --prefix TCLLIBPATH ' ' $out/lib/*
  +        --prefix TCLLIBPATH ' ' $out/lib/* \
  +        ${stdenv.lib.optionalString stdenv.isDarwin "--prefix DYLD_LIBRARY_PATH : $out/lib/expect${version}"}
       done
     '';
   
  
positive.code: { stdenv, fetchurl, tcl, makeWrapper }:
  
  let version = "5.45";
  in
  stdenv.mkDerivation {
    name = "expect-${version}";
  
    src = fetchurl {
  
negative.code:     description = "A tool for automating interactive applications";
      homepage = http://expect.nist.gov/;
      license = "Expect";
      platforms = platforms.unix;
      maintainers = with maintainers; [ wkennington ];
    };
  }
  