[Caml-list] camlp4: How to hook into the char stream of an existing grammar?

[Caml-list] camlp4: How to hook into the char stream of an existing grammar?

[Hendrik Tews]

Hi,

I have the following question: Suppose I use camlp4 with a
predefined grammar (such as pa_o.cmo). Is it possible to install
a function that intercept the character stream that flows into
the lexer of camlp4 (for instance to record the positions of
newlines)?

At the moment I only see the following solution: Copy
plexer.{ml,mli} from the ocaml sources, change Plexer.gmake
(keeping its interface) and use camlp4 ./plexer.cmo ...

Bye,

Hendrik
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Re: [Caml-list] camlp4: How to hook into the char stream of an existing grammar?

[Daniel de Rauglaudre]

Hi,

On Wed, Oct 30, 2002 at 07:33:20PM +0100, Hendrik Tews wrote:
> 
> I have the following question: Suppose I use camlp4 with a
> predefined grammar (such as pa_o.cmo). Is it possible to install
> a function that intercept the character stream that flows into
> the lexer of camlp4 (for instance to record the positions of
> newlines)?

You can patch the function which is called to parse implementations,
which is Pcaml.parse_implem. It is a reference which is defined by
default as: Grammar.Entry.parse Pcaml.implem.

Try the below file "foo.ml" as syntax extension:
     ocamlc -c -I +camlp4 foo.ml

This command prints the positions of newlines in file bar.ml:
     camlp4o ./foo.cmo pr_null.cmo bar.ml

------------------------------------------
(* file foo.ml *)
let f cs =
  let mycs =
    Stream.from
      (fun i ->
         try
           let c = Stream.next cs in
           if c = '\n' then begin
             Printf.eprintf "newline at pos %d\n" i;
             flush stderr;
           end;
           Some c
         with
           Stream.Failure -> None)
  in
  Grammar.Entry.parse Pcaml.implem mycs
;;

let _ = Pcaml.parse_implem := f
------------------------------------------

-- 
Daniel de RAUGLAUDRE
http://cristal.inria.fr/~ddr/
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