How to use ppx "by hand"?

Ecosystem
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1

I am trying to use some ppx in files that are compiled by bucklescript. bsb doesn’t have a very good support for ppx. So I have to do things “by hand” and the old way, as bucklescript is using ocaml 4.02.3. I think that the question is not bucklescript specific thought. It is more about how ppx are working in general.

bsb configuration expects a path to a ppx or a script and will apply it to every file. In my case, I don’t have my own ppx. The goal is to use ppx_deriving with some plugins and later some other existing ppx. So a script is used. It works fine when using annotation like [@@deriving ord].

`ocamlfind query ppx_deriving`/ppx_deriving \
`ocamlfind query ppx_deriving`/ppx_deriving_show.cma \
`ocamlfind query ppx_deriving`/ppx_deriving_ord.cma \
`ocamlfind query ppx_deriving`/ppx_deriving_eq.cma \
`ocamlfind query ppx_deriving`/ppx_deriving_map.cma \
`ocamlfind query ppx_deriving`/ppx_deriving_make.cma \
$@

Now I’d like to add ppx_enumerate`. If I understand correctly, ppx_enumerate is a plugin to ppx_deriving. So I thought that adding a few cma to the previous script would work without problem. Here is what I came for to use ppx_enumerate:

`ocamlfind query ppx_deriving`/ppx_deriving \
`ocamlfind query ppx_core`/ppx_core.cma \
`ocamlfind query ppx_optcomp`/ppx_optcomp.cma \
`ocamlfind query ppx_driver`/ppx_driver.cma \
`ocamlfind query ppx_type_conv`/ppx_type_conv.cma \
`ocamlfind query ppx_enumerate`/ppx_enumerate.cma \
$@

But when I try to compile my project using this script, I get an error:

Error: Cannot locate deriver enumerate

At this point I am stuck. I don’t know how to debug further.

  • How can I check what is really included in my ppx?
  • Am I calling ppx_deriving the good way?
  • Is it ok to use ppx_driver.cma with ppx_deriving? I saw in a few META files a message about ppx_driver. In ppx_optcomp for example: error(ppx_driver) = "Cannot use ppx_optcomp.for_ppx_deriving when ppx_driver is set"
  • What is the good documentation to read to understand all this?

Thanks for your help

2

Some progress so far.

I have been able to create a driver for ppx_enumerate this way:

ocamlfind opt -predicates ppx_driver -package ppx_enumerate -package ppx_deriving -package ppx_deriving.std -linkpkg -linkall -o ppx_driver ppx_driver_runner.cmxa

Then I use it as ./ppx_driver -as-ppx

It is not possible to compile reason code by default. Because this driver doesn’t accept -no-check at the same time than -as-ppx. But after a small change of ppx_driver.113.33.04 it is ok.

Now my problem is that this driver doesn’t accept annotation like [@@deriving enumerate, ord]. It stops with this error:

Error: ppx_type_conv: 'ord' is not a supported type type-conv generator