RE: [Caml-list] camlp4 & OCaml 4.08

["David Allsopp" <dra-news@metastack.com>]

Richard W.M. Jones wrote:
> On Sat, Jun 29, 2019 at 10:17:02AM +0000, David Allsopp wrote:
> > > On 29 Jun 2019, at 10:44, Richard W.M. Jones <rich@annexia.org> wrote:
> > >
> > >> On Sat, Jun 29, 2019 at 10:06:15AM +0100, Anil Madhavapeddy wrote:
> > >>> On 27 Jun 2019, at 14:45, Richard W.M. Jones <rich@annexia.org>
> > >>> wrote:
> > >>>
> > >>>
> > >>> I know camlp4 is dead and all that, but we've got some software
> > >>> which still uses it.  I will probably port it to camlp5 when I
> > >>> have the time, but has anyone got the patch to make camlp4 work with
> > >>> 4.08?
> > >>
> > >>
> > >> To fork the thread slightly,  how big are the camlp4 dependencies
> > >> remaining in your codebase, and is there anything we can do to help
> > >> migrate?
> > >
> > > The dependencies that I care about run through ocaml-gettext.
> > > Gettext is a specific method to make code internationalized and by
> > > its nature it involves deep changes throughout our codebase, so
> > > porting away from ocaml-gettext isn't an option any time soon.
> > > However porting ocaml-gettext to use something else might be.
> > >
> > > ocaml-gettext has a tool which runs over the OCaml source code and
> > > extracts the magic translatable strings, and it's my understanding
> > > that this is the only reason it uses camlp4.  AIUI this cannot be
> > > done using ppx's (maybe I'm wrong about that?) but could be done
> > > using camlp5.  In fact it was me who did the original port of
> > > ocaml-gettext from old camlp4 (ie. camlp5) to camlp4(!)
> >
> > It’s not instantly clear to my (non-expert) eyes why this can’t be done
> with PPX. If I read the camlp4 script correctly, it doesn’t introduce any
> new syntax, it just matches on particular function calls and rewrites
> them?
> 
> Actually I believe it simply extracts the string parameters into a
> separate file (from where they get translated).  However it's a separate
> tool, it doesn't run as part of ordinary compilation.

As I say, I've not done it, but walking an AST to pattern match those things sounds eminently doable. Similarly, I've not done it, but producing a driver program is one of the raison d'etre of ppxlib (or ppx-driver, as was).


David