Excerpts from Hezekiah M. Carty's message of Sun Sep 16 04:36:23 +0200 2007:
> I have been unable to get ocamlbuild to preprocess a single .ml file
> when creating an inferred interface file.  Here is some simple code
> to illustrate the problem:
> 
> test.ml:
> value f x = x + 2;
> 
> _tags:
> <test.ml>: pp(camlp4r)

Using pp(...), is not the best way to use preprocessors.

Try the camlp4r tag:

"test.ml": camlp4r

[...]

> I have also tried creating a myocamlbuild.ml to get around this, but
> using something like this in myocamlbuild.ml:
> 
> flag ["use_openin"]
>   (S [A "-I"; A "+camlp4"; A "-pp"; A "camlp4o pa_openin.cmo"]);;

You  certainly don't want to add these flags to any commands that treat a file
that  is  tagged  use_openin.  You  certainly  want to add them only for ocaml
preprocessing.

flag ["ocaml"; "pp"; "use_openin"]
     (A"pa_openin.cmo");;

> along with a matching flag in _tags causes havoc, with each of the
> items on the list being repeated twice and quoted, leading to shell
> errors.
> 
> I'm using revised syntax here as a simple example.  I originally ran
> in to this issue while trying to build a library which uses the
> pa_openin camlp4 extension.
> 
> Any suggestions or pointers on how to proceed with this?

HTH,
-- 
Nicolas Pouillard aka Ertai