[Caml-list] Ocamllex/Ocamlyacc feature request

[Caml-list] Ocamllex/Ocamlyacc feature request

[Brian Hurt]

Flex and Bison have an option to automatically output debugging
information to stdout in the generated code.

For flex, the option is -d, and documented thusly:

>       -d     makes the generated  scanner  run  in  debug  mode.
>              Whenever  a  pattern  is  recognized and the global
>              yy_flex_debug is non-zero (which is  the  default),
>              the  scanner  will  write  to  stderr a line of the
>              form:
>
>                  --accepting rule at line 53 ("the matched text")
>
>              The line number refers to the location of the  rule
>              in  the  file  defining the scanner (i.e., the file
>              that was fed to flex).  Messages are also generated
>              when  the  scanner  backs  up,  accepts the default
>              rule, reaches the  end  of  its  input  buffer  (or
>              encounters  a  NUL; at this point, the two look the
>              same as far as the scanner's concerned), or reaches
>              an end-of-file.

The Bison option is -t, and documented thusly:

>    Each step taken by the parser when `yydebug' is nonzero produces a
> line or two of trace information, written on `stderr'.  The trace
> messages tell you these things:
>
>    * Each time the parser calls `yylex', what kind of token was read.
>
>    * Each time a token is shifted, the depth and complete contents of
>      the state stack (*note Parser States::.).
>
>    * Each time a rule is reduced, which rule it is, and the complete
>      contents of the state stack afterward.

These are incredibly usefull for debugging your parsers.

Brian


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Re: [Caml-list] Ocamllex/Ocamlyacc feature request

[Ken Wakita]

You can turn the parser trace facility on by:
setenv OCAMLRUNPARAM "p"

Read the OCAMLRUNPARAM section in:
http://caml.inria.fr/ocaml/htmlman/manual024.html

Ken Wakita

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Re: [Caml-list] Ocamllex/Ocamlyacc feature request

[Damien]

Hello,

OCAMLRUNPARAM seems pretty fine for debugging purposes, 
what about "end-user error reporting" :

could the special terminal 'error' have some useful parameters ?

>type token_error_t = {
>chars: int*int;
>lexeme: string;
>token: token;
>expected: token list;
>}
>"%token <token_error_t> error"
would allow
>toto:
>| ... | ...
>| error { failwith (arf $1) }
>;

then, is there a "nice method" to insert error terminals in a
grammar, in order to get a parser :
	- without s/r or r/r conflicts
	- that never raise "Parsing.parse_error" : all error cases are
	identified and raise "My_informative_parse_error"
?

till now, I've always used the "try until no conflict" method, which
isn't really "nice"

could ocamlyacc decide whether a grammar is "exhaustive", like ocaml
does for pattern-matching ?


thanks,
damien

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Re: [Caml-list] Ocamllex/Ocamlyacc feature request

[Luc Maranget]

> 

> does for pattern-matching ?
> 
> 
> thanks,
> damien
> 


Well, such a test is probalbly needed for both lex and yacc !


In the ocamllex case, this is quite easy as regards theory, since the
test can be  performed on automata.

The same may apply to yacc automata.

--Luc

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[Caml-list] Syntax error

[Lukasz Lew]

Hi.

I am using Genlex and ocaml streams and parsers. And when I catch 
exception Stream.Error "", I can not generate other message than "syntax error".

How can I obtain informations about line number or character number, 
where the error ocurred ?

In ocaml examples at http://caml.inria.fr/Examples/oc.tar.gz, function 
pos_in is used, but it returns always number of last character in stream.

Do you have any ideas?
And how ocamlyacc deals with this problem?

Regards,
Lukasz Lew

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Re: [Caml-list] Syntax error

[Stefan Heimann]

Hi,

On Wed, Jun 04, 2003 at 11:19:47AM +0200, Lukasz Lew wrote:
> Hi.
> 
> I am using Genlex and ocaml streams and parsers. And when I catch 
> exception Stream.Error "", I can not generate other message than "syntax error".
> 
> How can I obtain informations about line number or character number, 
> where the error ocurred ?
> 
> In ocaml examples at http://caml.inria.fr/Examples/oc.tar.gz, function 
> pos_in is used, but it returns always number of last character in stream.

I don't have a good solution for this, just a hack. 

I have something like 'let lineno = ref 1' in the lexer and increment
the lineno everytime a '\n' is read. In the parser I have written the
parse_error function like that:

let parse_error s = raise Parse_error

My main program looks like that:

(* raises End_of_file if i is too large *)
let rec get_line i cin =
  begin
    assert (i >= 1);
    let l = input_line cin in
      if i == 1 then l
      else get_line (i - 1) cin
  end

let _ =
  let fname = Sys.argv.(1) in
  let lexbuf = Lexing.from_channel (open_in fname) in
    try
      let gr = Ebnf_parser.grammar Ebnf_lexer.token lexbuf in
        print_string (Grammar.string_of_grammar gr)
    with Parsing.Parse_error ->
      begin
        prerr_string (fname ^ ":" ^ (string_of_int !Ebnf_lexer.lineno)
                      ^ ": ");
        prerr_string ("Syntax error on token `" 
                      ^ (Lexing.lexeme lexbuf) ^ "'.");
        prerr_newline ();
        try let l = get_line !Ebnf_lexer.lineno (open_in fname) in
          prerr_string l;
          prerr_newline ();
        with End_of_file -> ()
      end

Maybe this helps...

Bye,
  Stefan

-- 
Stefan Heimann
http://www.stefanheimann.net :: personal website.
http://cvsshell.sf.net       :: CvsShell, a console based cvs client.

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