From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <ecc@cmu.edu>
X-Original-To: caml-list@yquem.inria.fr
Delivered-To: caml-list@yquem.inria.fr
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39])
	by yquem.inria.fr (Postfix) with ESMTP id 81383BDE6
	for <caml-list@yquem.inria.fr>; Sat, 10 Sep 2005 16:15:15 +0200 (CEST)
Received: from ux9.sp.cs.cmu.edu (UX9.SP.CS.CMU.EDU [128.2.220.166])
	by concorde.inria.fr (8.13.0/8.13.0) with SMTP id j8AEFEf1008669
	for <caml-list@yquem.inria.fr>; Sat, 10 Sep 2005 16:15:15 +0200
Received: from c-24-3-154-200.hsd1.pa.comcast.net ([24.3.154.200])
          by ux9.sp.cs.cmu.edu id aa23629; 10 Sep 2005 10:14 EDT
Received: from ecc by stratocaster.home with local (Exim 4.52)
	id 1EE688-0002ty-3y
	for caml-list@yquem.inria.fr; Sat, 10 Sep 2005 10:14:56 -0400
Date: Sat, 10 Sep 2005 10:14:56 -0400
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] ocamlyacc help
Message-ID: <20050910141455.GA11148@localhost>
Mail-Followup-To: caml-list@yquem.inria.fr
References: <ad8cfe7e05091003403ac29028@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ad8cfe7e05091003403ac29028@mail.gmail.com>
User-Agent: Mutt/1.5.9i
From: Eric Cooper <ecc@cmu.edu>
X-Miltered: at concorde with ID 4322EA72.000 by Joe's j-chkmail (http://j-chkmail.ensmp.fr)!
X-Spam: no; 0.00; caml-list:01 ocamlyacc:01 char:01 lalr:01 parsing:01 token:01 char:01 token:01 expr:01 expr:01 lalr:01 parsers:01 stack:01 ocaml:01 wrote:01 

On Sat, Sep 10, 2005 at 10:40:28PM +1200, Jonathan Roewen wrote:
> I want to parse a string of format:
> 
> (OP FLOAT*)* and generate a (char * float list) list.
> 
> The problem I have is I don't know how to generate further tuples.

(Re)read the Dragon book on LALR parsing!

%token <char>	OP
%token <float>	FLOAT

%start expr
%type <(char * float list) list> expr

%%

expr:
	op_list				{ List.rev $1 }
;

op_list:
	/* empty */			{ [] }
  |	op_list OP float_list		{ ($2, List.rev $3) :: $1 }
;

float_list:
	/* empty */			{ [] }
|	float_list FLOAT		{ $2 :: $1 }
;

Note that it's good practice to write rules for "lists of things" in a
left-recursive style, because that allows LALR parsers to handle
arbitrarily-long lists without stack overflow.  In OCaml, where the
natural semantic action for a list is to build a list, you probably want
to build the list backwards (i.e. $2 :: $1 instead of $1 @ [$2]),
and then reverse it where it's used (if that's even necessary).

-- 
Eric Cooper             e c c @ c m u . e d u