Re: [Caml-list] Ocaml compiler documentation

[Mark Shinwell <mshinwell@janestreet.com>]

Alain, I think "open!" does affect the "unused open" warning.  (This
is a useful feature when you are trying to establish a consistent set
of in-scope names, a good example being Core's "open
Int.Replace_polymorphic_compare", which you may well want to have even
if your file doesn't happen to use a comparison operator right now.)

I checked this using the following test program and "-w +a".

module M = struct
  let foo x = x + 42
end
open! M         (or "open")

Mark

On 3 April 2014 21:16, Alain Frisch <alain@frisch.fr> wrote:
> On 4/3/2014 4:48 AM, Yotam Barnoy wrote:
>>
>> Ok I think a good place to start a tour of the compiler is in
>> parsing/parsetree.mli. This file is actually very well documented, with
>> terse but effective examples of almost every constructor and type.
>
>
> Good idea indeed, especially that the Parsetree will gain in the next
> release a more important status, with -ppx rewriters, annotations and
> attributes.
>
>
>> I had to refer to the OCaml manual for a few of the corner cases. For
>> example, I didn't know about the #class type shortcut. I think a few
>> comments explaining the more obscure facets of the language could be
>> helpful.
>
>
> Generally speaking, a good place to document the language is the user
> manual.  Don't hesitate to suggest patches to the manual as well!  (The
> source code is in the same repository:
> http://caml.inria.fr/cgi-bin/viewvc.cgi/ocamldoc/trunk/ ).
>
> That said, for the specific case of Parsetree, it might indeed be useful to
> give some hints about rare language features in the source code as well.
>
>
>> 1. What is the difference between an extension and an attribute? From
>> what I understand, they are both means of integrating additional
>> metadata into the AST that can then be parsed by implementations of the
>> ast-mapper, but why are there 2 mechanisms?
>
>
> An extension is something which will be rejected by the type-checker. It is
> placeholder for "sub-languages", to be processed by -ppx filters.
>
> An attribute is indeed a way to integrate meta-data into a (hopefully) valid
> AST.  They could be used by -ppx filters to drive their behavior, by
> external tools to get some extra information (e.g. Bisect annotations), and
> they are propagated to the typedtreed, and hence to .cmt/.cmti files, again
> for external tools which read those files.  They are also kepts on some
> kinds of declarations (e.g. values and types) so that they are part of the
> Types structures, and hence found in .cmi files as well.  The compiler also
> give a built-in meaning to some attributes (to be documented).
>
> Some more information:
> http://caml.inria.fr/cgi-bin/viewvc.cgi/ocaml/trunk/experimental/frisch/extension_points.txt?revision=HEAD&view=markup
>
>
>> 3. line 684: what is the purpose of the override flag on Pstr_open? It's
>> not explained by the comment.
>
>
> The override flag (i.e. "open!" as opposed to "open") is used to silence the
> new warning which signals when an open statement shadows an existing
> identifier which is later used.   (It does not affect the 'unused open'
> warning.)
>
>
>> 4. The toplevel phrases are not clear. What is the purpose of Ptop_dir
>> on line 721?
>
>
> Those are #-directives understood by the toplevel (#use, #load, etc).
>
>
> -- Alain
>
>
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