Sylvain Le Gall wrote:
> May I recommend you to write this in a more simple way:
>
> -------------------------------------------------------------------------
> rule lex =
>   parse eof    { () }
>   | "(*"       { start := pos lexbuf; lexNestComment lexbuf; lex lexbuf }
>
> and lexNestComment =
>   parse eof    { error (loc 2) "unterminated comment" }
> | "(*"         { lexNestComment lexbuf }
> | "*)"         { () }
> | _            { lexNestComment lexbuf }
> -------------------------------------------------------------------------
>   

Mh, I think in lexNestComment it should at least say

 | "(*"         { lexNestComment lexbuf; lexNestComment lexbuf }


That might work. I am not sure how well the various lexer generators 
handle arbitrary recursive invocations and reentrance, though. Have you 
tried it? If it works, yes, that's certainly a nicer version.

- Andreas