anchor.diff:  
       for cmd in $out/bin/* ; do
         wrapProgram "$cmd" \
  -        --set TCLLIBPATH "${tcl}/${tcl.libdir}" \
           --set TK_LIBRARY "${tk}/lib/${tk.libPrefix}"
       done
     '';
  
positive.code:   };
  
    nativeBuildInputs = [ makeWrapper ];
    buildInputs = [ tcl tk libX11 zlib ];
  
    prePatch = ''
      sed -i -e '/^ *set headerPath *{/a ${tcl}/include ${tk}/include' \
  
negative.code:     platforms = lib.platforms.linux;
    };
  }
  