Re: [Caml-list] working %.pp.ml target with ocamfind/ocamlbuild

[Anil Madhavapeddy <Anil@recoil.org>]

On Sun, Sep 09, 2012 at 05:29:53PM +0100, Wojciech Meyer wrote:
> Gabriel Scherer <gabriel.scherer@gmail.com> writes:
> 
> > This is useful for debugging purposes, and for some (minor) modes of
> > use of Camlp4. However, for most Camlp4 development, this has the
> > severe downside of losing the location information of the original
> > file, if I understand correctly. This means that you don't want to use
> > it as a transparent step towards compilation, but only in exceptional
> > situations where the developers will re-edit the output code.
> 
> I think I've to say I disagree it's not useful, when I'm developing a
> syntax extension on top of Camlp4 I really want to see the generated
> code. Moreover to understand some of the more complicated syntax
> extensions like type_conv, deriving, FoldGenerator I need to look at the
> expanded code to understand how to use it - last time I hit the same
> problem it was actually 'deriving-ocsigen' when I needed to implement my
> own Show module - it's just much faster to see what's being generated
> for the usual case, then trying to figure out from the recipe in the
> documentation.  Otherwise for bootstrapping purposes, you might want to
> pre-generate some code too and put into the repository.

The %.pp.ml rule is really essential for day-to-day development too.
Since camlp4 cannot generate ocamldoc comments, it's often easier to just
dump the .pp.ml output and inspect the code directly, rather than root
around figuring out what the code generator modules are doing.

This is less of an issue with well-established extensions such as sexplib,
but useful when learning new ones such as the Lwt one (which has some odd
corner cases such as the >> bind precedence).

-- 
Anil Madhavapeddy                                 http://anil.recoil.org