anchor.diff:  assert config != null -> configFile == null;
   
   let
  -  inherit (stdenv.lib)
  +  inherit (lib)
       optionalString;
   
     configFile' =
  
positive.code: in
  stdenv.mkDerivation rec {
    name = "st-0.7";
    
    src = fetchurl {
      url = "http://dl.suckless.org/st/${name}.tar.gz";
      multihash = "QmV1FssAdXN44hWi4QjWp5GLn5ZqwqnvBjJ8JRNayMRi5Z";
  
negative.code:   preBuild = optionalString (configFile' != null) ''
      cp ${configFile'} config.def.h
    '';
  
    buildInputs = [
      freetype
      fontconfig
      libx11
      libxext
      libxft
      libxrender
      ncurses
      xorgproto
    ];
  
    preInstall = ''
      export TERMINFO="$out/share/terminfo"
      installFlagsArray+=("PREFIX=$out")
    '';
  
    meta = with lib; {
      homepage = http://st.suckless.org/;
      license = licenses.mit;
      maintainers = with maintainers; [
  