Re: [Caml-list] camlp4 & OCaml 4.08

[Louis Gesbert <louis.gesbert@ocamlpro.com>]

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For what it's worth, Learn-OCaml [1] uses a rather straightfoward way to handle translations through PPX, based on the gettext format.

It's a quick hack and the build-system around it could use some cleanup, though, which is the reason why it wasn't released as a library: please consider it a proof of concept that PPX can be used for gettext.

- Translatable strings are introduced through [%i "Blah" ] (or [%if "Blah"] for format-strings; advanced uses like changing format parameters order are not supported)

- The build extracts these to a separate file at build-time, based on an environment variable `DUMP_POT` [2]. Probably the most dirty part here, and it requires a clean build, but it works...

- Then the standard GNU tools can be used to manage the translations [3]

- There is a tiny library at runtime that allows choosing the locale; located strings are rewritten to arrays with a lookup based on it (but changing that to something more elaborate like using external resource files should be pretty straightforward) [4].

Louis Gesbert -- OCamlPro

[1] https://github.com/ocaml-sf/learn-ocaml/
[2] https://github.com/ocaml-sf/learn-ocaml/blob/master/src/utils/ppx_ocplib_i18n.ml
[3] https://github.com/ocaml-sf/learn-ocaml/blob/master/Makefile#L33
[4] https://github.com/ocaml-sf/learn-ocaml/blob/master/src/utils/ocplib_i18n.mli

> - Richard W.M. Jones, 29/06/2019 10:43 -
> 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(!)
> 
> (see libgettext-ocaml/pr_gettext.ml in the OCaml sources)
> 
> > It's pretty exhausting trying to keep camlp4 maintained with a skeleton
> > crew, and there appears to be a stubborn tail of packages which aren't
> > migrating despite it having been quite a few years since the deprecation.
> 
> I agree, however also changing working code is always a pain and
> there's never a good time.
> 
> Rich.
> 

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