[Caml-list] debugging an ocamlyacc parser

[Caml-list] debugging an ocamlyacc parser

[Rafael 'Dido' Sevilla]

Well, while my current ocamlyacc parser seems to be working pretty well,
I'm just wondering if there's a debug mode available for
ocamlyacc-generated parsers, like the debugging mode that Bison uses
when you do a #define YYDEBUG, printing out all the states the parser
goes through as it receives tokens from the lexer, so along with the
generated y.output file I can see how it's working (or not working as
the case may be).

-- 
Rafael R. Sevilla <sevillar@team.ph.inter.net>   +63(2)   8177746 ext. 8311
Programmer, Inter.Net Philippines                +63(917) 4458925
http://dido.engr.internet.org.ph/                OpenPGP Key ID: 0x5CDA17D8
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RE: [Caml-list] debugging an ocamlyacc parser

[Mattias Waldau]

I normally test the lexer and the parser separately.

The lexer is easy to test using a function like:

  let lexbuf = Lexing.from_channel file_channel in
  let result = ref [] in
  try
    while true do
      let next_token = Dtd_lexer.token lexbuf in
      result := next_token :: !result;
      if debug_lexer then Dtd_types.print next_token;
      if next_token = Dtd_types.EOF then raise Not_found
    done;
    List.rev (!result)
  with Not_found -> List.rev (!result)

For debugging the parser I set the -v flag to ocamlyacc and look at the
.parser file

/mattias

> -----Original Message-----
> From: owner-caml-list@pauillac.inria.fr
> [mailto:owner-caml-list@pauillac.inria.fr]On Behalf Of Rafael 'Dido'
> Sevilla
> Sent: Tuesday, October 23, 2001 4:15 AM
> To: Caml List
> Subject: [Caml-list] debugging an ocamlyacc parser
>
>
> Well, while my current ocamlyacc parser seems to be working pretty well,
> I'm just wondering if there's a debug mode available for
> ocamlyacc-generated parsers, like the debugging mode that Bison uses
> when you do a #define YYDEBUG, printing out all the states the parser
> goes through as it receives tokens from the lexer, so along with the
> generated y.output file I can see how it's working (or not working as
> the case may be).
>
> --
> Rafael R. Sevilla <sevillar@team.ph.inter.net>   +63(2)   8177746
> ext. 8311
> Programmer, Inter.Net Philippines                +63(917) 4458925
> http://dido.engr.internet.org.ph/                OpenPGP Key ID:
> 0x5CDA17D8
> -------------------
> Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ:
http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives:
http://caml.inria.fr

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Re: [Caml-list] debugging an ocamlyacc parser

[Hendrik Tews]

Hi,

Rafael 'Dido' Sevilla writes:
   Date: Tue, 23 Oct 2001 10:14:42 +0800
   Subject: [Caml-list] debugging an ocamlyacc parser
   
   I'm just wondering if there's a debug mode available for
   ocamlyacc-generated parsers, like the debugging mode that Bison uses
   when you do a #define YYDEBUG, printing out all the states the parser

   
I was also missing the YYDEBUG. My workaround looks as follows:

In the header of grammar.mly:

  let d s =
    if debug_level _DEBUG_PARSER
    then begin
      prerr_string ("REDUCE " ^ s ^ "\n");
      flush stderr
    end;;

a typical rule looks like 

    signaturetype:
	TYPE ID	 		{ d "signaturetype";
				  do_sig_type_decl $2;
			        }
    ;

The lexer uses the same schema:

  let d s =
    if debug_level _DEBUG_LEXER
    then begin
      prerr_string ("SHIFT " ^ s ^ "\n");
      flush stderr
    end

and 

     | '='			{ d "Equal"; 
				  EQUAL }


_DEBUG_PARSER and _DEBUG_LEXER are constants and the return value
of the debug_level function can be influenced via a command line
switch.

Bye,

Hendrik
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Re: [Caml-list] debugging an ocamlyacc parser

[Xavier Leroy]

> Well, while my current ocamlyacc parser seems to be working pretty well,
> I'm just wondering if there's a debug mode available for
> ocamlyacc-generated parsers, like the debugging mode that Bison uses
> when you do a #define YYDEBUG, printing out all the states the parser
> goes through as it receives tokens from the lexer, so along with the
> generated y.output file I can see how it's working (or not working as
> the case may be).

There is such a debugging mode in the pushdown automaton used to
execute ocamlyacc parsers, but it is not easily accessible.

You need to build the "debug" version of the bytecode interpreter (cd
runtime ; make ocamlrund), then run your bytecode executable with
"ocamlrund -P myprog".

You then get a trace of shift and reduce actions; tokens read are also
printed, but in such a low-level format that it's nearly useless...

I agree this tracing facility should be made better at some point,
although printing tokens correctly is difficult in general.

- Xavier Leroy
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