[Caml-list] Porting old-style ppx to driver-style?

[Caml-list] Porting old-style ppx to driver-style?

[Paul A. Steckler]

There's a nice OCaml library, available via OPAM as "lens", which
allows deriving lenses for record types.

By adding the following clause in a jbuild file, the ppx works fine:

  (preprocess (action (run ppxfind -legacy
lens.ppx_deriving,ppx_deriving.std --as-pp ${<})))

But adding "ppx_inline_test" to this clause doesn't allow an
"(inline_tests)" clause to work, and when building a library, only one
"preprocess" clause appears to have an effect.

Using the ppx within a "(preprocess (pps ...))" clause does not
succeed. So I can have lenses, or inline tests, but not both.

I believe the solution is to turn the ppx into a new-style "driver".
What's the best way to do that? Is it as simple as changing the build
to use a jbuild as described in the section "Creating a new Ppx_driver
based rewriter"?:

  https://github.com/janestreet/ppx_driver

Do I need to make any other code changes?

-- Paul

Re: [Caml-list] Porting old-style ppx to driver-style?

[Rudi Grinberg]

Hi Paul,

> I believe the solution is to turn the ppx into a new-style "driver".
> What's the best way to do that? Is it as simple as changing the build
> to use a jbuild as described in the section "Creating a new Ppx_driver
> based rewriter"?:

Using ppx_driver (now a part of ppxlib I believe) isn't necessary. I
think it should be enough to follow the lead of other ppx_deriving
plugins that are built with dune (ppx_deriving_yojson for example). The
necessary bit here is to use omp and generate a correct META file that
will make ppx_deriving_lens usable in driver *and* as a dynlinked
deriver for ppx_deriving itself.

There's an existing PR to port ocaml-lens and I believe it's on the
right track:

https://github.com/pdonadeo/ocaml-lens/pull/9

Perhaps you can help out with that effort?

Cheers,

Rudi.

Re: [Caml-list] Porting old-style ppx to driver-style?

[Paul A. Steckler]

On Thu, May 10, 2018 at 3:00 AM, Rudi Grinberg <rudi.grinberg@gmail.com> wrote:
> There's an existing PR to port ocaml-lens and I believe it's on the
> right track:
>
> https://github.com/pdonadeo/ocaml-lens/pull/9
>
> Perhaps you can help out with that effort?

In fact, I'm using that code (and my colleague submitted it).

Thanks for the clarification.

-- Paul