Re: [Caml-list] Compiling with camlp4 extensions

[Gabriel Scherer <gabriel.scherer@gmail.com>]

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