Dear camlers,

I'm currently trying to implement a camlp4 quotation whose contents will be
parsed using ocamllex and menhir. Everything went unexpectedly well until I
tried to add antiquotations. Following Tiphaine Turpin's format syntax
extension (https://forge.ocamlcore.org/projects/format/), an antiquotation
is parsed as a token in ocamllex, and this token is defined in my parser as:

%token <Camlp4.PreCast.Syntax.Ast.expr> EXPR

The thing is when I try to compile my project with ocamlbuild I get the
following error:

[gesundheit:~/w/ocaml-r 14:46]$make
ocaml setup.ml -build
Finished, 0 targets (0 cached) in 00:00:00.
+ menhir --ocamlc 'ocamlfind ocamlc -I src/syntax' --infer
src/syntax/r_lang_parser_y.mly
File "src/syntax/r_lang_parser_y.mly", line 7, characters 40-44:
Warning: the token EXPR is unused.
File "src/syntax/r_lang_parser_y.mly", line 7, characters 8-38:
Error: Unbound module Camlp4
...

Now I can easily (but manually) fix this by adding the missing -I option
for camlp4 libs:

[gesundheit:~/w/ocaml-r/_build 15:22]$menhir --ocamlc 'ocamlfind ocamlc -I
src/syntax -I +camlp4' --infer src/syntax/r_lang_parser_y.mly
File "src/syntax/r_lang_parser_y.mly", line 7, characters 40-44:
Warning: the token EXPR is unused.
[gesundheit:~/w/ocaml-r/_build 15:22]$

My question is how do I tell ocamlbuild to add this option directly? I fear
the response is "you cannot", if I refer to the piece of code in ocamlbuild
that generates the call to menhir:

let menhir mly env build =
  let mly = env mly in
  let menhir = if !Options.ocamlyacc = N then V"MENHIR" else
!Options.ocamlyacc in
  Ocaml_compiler.prepare_compile build mly;
  Cmd(S[menhir;
        A"--ocamlc"; Quote(S[!Options.ocamlc; ocaml_include_flags mly]);
        T(tags_of_pathname mly++"ocaml"++"parser"++"menhir");
        A"--infer"; Px mly])

I fail to see in this function a hook which I could use to inject the
missing argument. Would any one know a workaround to use tokens that have
hold a value whose type is not defined in the standard library?

Cheers,
  Philippe.