ocamlPackges.ppx_tools: fix evaluation for OCaml ≥ 5.2

{ lib, stdenv, fetchFromGitHub, buildDunePackage, ocaml, findlib, cppo }:

if lib.versionAtLeast ocaml.version "5.2"

then throw "ppx_tools is not available for OCaml ${ocaml.version}"

else

let param =

  let v6_6 = {

    version = "6.6";

  buildDunePackage {

    inherit pname src meta;

    inherit (param) version buildInputs nativeBuildInputs;

    duneVersion = "3";

  }

else

  stdenv.mkDerivation {