Re: [Caml-list] Compiling with camlp4 extensions

[Aaron Bohannon <bohannon@seas.upenn.edu>]

Ah, yes.  That is helpful.  I had thought of trying to "extend" OCaml
by replacing the grammar with a different one, although I didn't know
exactly how to do it.

Of course, it seemed obvious to me that I wouldn't be able to use my
own lexer if I did that.  I'm not sure if I will want to do that or
not yet, but I was thinking I would just learn to do it that way so
I'd have that flexibility if I need it.  Unfortunately, the page stops
short of explaining how to pursue that approach. :(

 - Aaron

On Sat, Jun 23, 2012 at 3:42 AM, Gabriel Scherer
<gabriel.scherer@gmail.com> wrote:
> See the "full parser tutorial" in the Camlp4 wiki, it has information
> for what, if I have correctly understood, is your use case, including
> location handling.
>  http://brion.inria.fr/gallium/index.php/Full_parser_tutorial
>
> On Sat, Jun 23, 2012 at 2:43 AM, Aaron Bohannon <bohannon@seas.upenn.edu> wrote:
>> Thanks for the reply.  The example is helpful.  However, I should have
>> been more clear: I don't exactly want to write a syntax extension, per
>> se.  Rather, I am trying to use camlp4 to parse a non-OCaml grammar
>> and to generate an OCaml AST.  So the "Register.OCamlSyntaxExtension"
>> functor doesn't seem like it will work for me.  Instead, I tried using
>> "Printers.Ocaml.print_implem" in my "extension" code and everything
>> works fine, except for error locations.  Of course, I realize this is
>> because the AST is being printed and then re-parsed, but I don't know
>> how to prevent it from being reparsed.  I looked through all the
>> Camlp4 interfaces and thought that perhaps I need to use the function
>> "Register.register_str_item_parser".  But I couldn't make that work.
>> Either that's not the function I need or else I don't know how to use
>> it -- I can't tell which.
>>
>>  - Aaron
>>
>> On Fri, Jun 22, 2012 at 10:36 AM, Gabriel Scherer
>> <gabriel.scherer@gmail.com> wrote:
>>> All nodes in a Camlp4 AST are annotated with location information; the
>>> locations you get from the parser are correct, and it is your
>>> responsibility, as an extension writer, to ensure that any new nodes
>>> you generate also have (approximately) correct location information.
>>>
>>> If you build AST nodes "by hand", you have to provide this location
>>> explicitly. If you use the concrete syntax quotations, the location
>>> used is the value _loc present in the environment, whatever it may be.
>>> So to have correct locations, you have to make sure that, at every AST
>>> you produce through a quotation, there is a "_loc" variable in scope
>>> with the correct value. If you match AST pieces with quotation
>>> patterns (match e with <:expr< $a$ + $b$ >> -> ...), you may bind the
>>> location variable through the syntax "<:expr@foo<", for example:
>>> (match e with <:expr@_loc< $a$ + $b$ >> -> ...). Finally, if you're
>>> inside an EXTEND block defining a parsing rule, the idenfitier _loc is
>>> implicitely bound to a location corresponding to what was parsed by
>>> this rule.
>>>
>>> See for example the toy extension pa_refutable, that has example of
>>> those various things:
>>>  http://bluestorm.info/camlp4/pa_refutable.ml.html
>>>
>>> In some very rare cases (or if you are perfectionist), you may want to
>>> give to a new node a location that is not quite the location of any of
>>> the parsed node you're working on. You may use various functions of
>>> the Loc submodule of your syntax definition to forge new locations; in
>>> particular, Loc.merge merges two (supposed contiguous) locations.
>>>  http://bluestorm.info/camlp4/camlp4-doc/Sig.Loc.html
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Jun 22, 2012 at 5:53 PM, Aaron Bohannon <bohannon@seas.upenn.edu> wrote:
>>>> Hi,
>>>>
>>>> I have been trying to use the new camlp4 to write an OCaml syntax
>>>> extension.  All the examples I have seen so far suggest that I use the
>>>> extension by passing ocamlc the "-pp" option.  But it seems that all the
>>>> location info for error messages gets lost when I do this unless I catch and
>>>> report the parse error myself within the extension.  Is there some way to
>>>> get ocamlc to report the parse error at the correct location automatically?
>>>>
>>>> - Aaron