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From: Luc Maranget <luc.maranget@inria.fr>
Message-Id: <200205130921.LAA0000013377@beaune.inria.fr>
Subject: Re: [Caml-list] Bug in typing polymorphic variants found
To: garrigue@kurims.kyoto-u.ac.jp (Jacques Garrigue)
Date: Mon, 13 May 2002 11:21:28 +0200 (MET DST)
Cc: skaller@ozemail.com.au, caml-list@inria.fr
In-Reply-To: <20020513154639Z.garrigue@kurims.kyoto-u.ac.jp> from "Jacques Garrigue" at mai 13, 2002 03:46:39 
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> I expect there is a bug somewhere in your program...
> 
> It is a good idea to make your makefiles to work with both ocamlc and
> ocamlopt, because ocamlc gives you much more debugging information.
> Some segmentation faults with ocamlopt give actually informative
> errors with ocamlc.
> 
> By the way, I got errors trying to compile felix, because there was an
> old src/flx_parse.ml, which should not be there.
> 

I did the same thing, and even ran felix under ocamldebug
(another reason to use both bytecode and native compilation)

1. I has to alter Flx_lex to compile
  (suppress a self reference to the Flx_lex module)

2. By running the example (run), until it crashed
   going back (back) in execution a little, and looking at the
   call stack (backtrace), I found the loop :


#52327  Pc : 242856  Flx_pretok char 6183
#52328  Pc : 242856  Flx_pretok char 6183
#52329  Pc : 242856  Flx_pretok char 6183
#52330  Pc : 242856  Flx_pretok char 6183
#52331  Pc : 242856  Flx_pretok char 6183
#52332  Pc : 242856  Flx_pretok char 6183
#52333  Pc : 242856  Flx_pretok char 6183

etc...


Apparently the loop is in module Flx_pretok :


let pre_tokens_of_lexbuf buf state =
  let lex_it() = Flx_lex.pre_flx_lex buf state in
  let run = ref true in
  let rec get () =
    if !run
    then let t = lex_it () in
      match t with
      | [Flx_parse.ENDMARKER] ->
        run := false;
        [Flx_parse.ENDMARKER]
      | _ -> t @ get() <------- HERE is the recursive call                 
    else [Flx_parse.ENDMARKER]
  in get ()


Hope it helps,


--Luc
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