Re: [Caml-list] About ocamlbuild

[Arnaud Spiwack <Arnaud.Spiwack@lix.polytechnique.fr>]

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Well,

I must say the sort of mafioso-like reasoning ­- "you really do not want to
do that" - doesn't really make sense to me.

Here are valid reasons not to include a feature X in a tool:

   - I don't have time to do X
   - I don't know how to do X
   - Having X would prevent me from having Y which I'd rather

Any other reason is bad.

People want to have tags and compilation pragmas? Well, let them, they
probably have valid reasons to (some options may be better seen global to
the project and other local to files). People want to interleave compiling
the build system and compiling the project. They have a good reason for
that too. Also: ocamlbuild doesn't only compile ocaml files.

Related to that last point, and to the initial question: as far as I'm
aware, an ocamlbuild plugin cannot depend on a custom library (to go around
that we can use a myocamlbuild.ml which compiles a mymyocamlbuild.ml (or
something) with the appropriate linking options, then copy it in a
_build_stage2 directory, then Unix.excv an ocamlbuild -no-plugin -build-dir
_build_stage2. It would be nice if there were a standard and simple way to
do this sort of thing). In particular there is no principled way to
distribute a tool together with an ocamlbuild library against which to
compile our myocamlbuild.ml plugins (hence extending what ocamlbuild can
"natively" compile).



On 15 November 2012 23:36, Xavier Clerc <xavier.clerc@inria.fr> wrote:

> ----- Mail original -----
> > On 11/15/2012 4:48 PM, Xavier Clerc wrote:
> > >> 3 - Finally, I find the idea of tags good, for backward
> > >> compatibility
> > >> reasons (you do not have to change your code), but not enough. For
> > >> instance, in haskell (and some compilers written in ocaml), you
> > >> can
> > >> add "tags" at the beginning of your files. You would start your
> > >> ocaml files with comments such as:
> > >>
> > >> (* #OPTIONS -rectypes *)
> > > Well, I find tags pretty convenient, and do not dislike the comment
> > > approach. However, I am pretty sure I do not want the related
> > > information
> > > to be scattered over multiple locations.
> > It's exactly this reason that I'm strongly in favor of magic comments
> > or
> > pragmas or something in .ml files to do do this kind of thing.
> > Splitting the data needed to compile a module into two parts: the
> > module
> > and a makefile (or _tags or OMakefile or whatever) seems a violation
> > of
> > your "multiple locations" policy.
>
> I do not follow your line of thought: every information about how to
> compile is clearly in build files, and not in source code files.
> If I wonder how the command-line for a given compilation is determined,
> there is only one place to look.
>
> Again, I do not claim that the current state of affairs (everything
> in build files) is better than a pure pragma-based solution (everything
> in source files). My objection is about a mixed system where one should
> have to consult both build and source file in order to know which
> options are passed to compile a given module.
>
>
> > While I grant that some
> > compilation
> > options (whether to compile in debug/profiling/native mode, location
> > of
> > external libraries) should not be included in a source file, I'm
> > strongly in favor of having the build system work out the details of
> > dependencies (internal to project and external, installed in global
> > location) and even what camlp4 to run based on the contents of the
> > file
> > itself and not elsewhere.
>
> To be fair, I should point out that Coq is extracting camlp4 information
> from source files in order to determine how to treat them.
>
>
> Just a final remark: compared to Haskell, OCaml compilers feature a limited
> number of command-line switches having an influence on the semantics of a
> source file(*). I regard this as a pleasant thing, and think this makes the
> issue at hand quite minor.
>
>
> Kind regards,
>
> Xavier Clerc
>
>
>
>
> (*) we are only talking about labels, applicative functors, and recursive
> types
>
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