From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <mle+ocaml@mega-nerd.com>
X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr
X-Spam-Level: 
X-Spam-Status: No, score=0.0 required=5.0 tests=none autolearn=disabled 
	version=3.1.3
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 CB704BC6B
	for <caml-list@yquem.inria.fr>; Wed, 21 Feb 2007 10:36:11 +0100 (CET)
Received: from smtp.syd.people.net.au (smtp.syd.people.net.au [218.214.225.98])
	by concorde.inria.fr (8.13.6/8.13.6) with SMTP id l1L9a8Nw027397
	for <caml-list@yquem.inria.fr>; Wed, 21 Feb 2007 10:36:10 +0100
Received: (qmail 5031 invoked from network); 21 Feb 2007 09:36:19 -0000
Received: from unknown (HELO coltrane.mega-nerd.net) (218.214.64.136)
  by smtp.syd.people.net.au with SMTP; 21 Feb 2007 09:36:19 -0000
Received: from coltrane (coltrane [192.168.1.101])
	by coltrane.mega-nerd.net (Postfix) with SMTP id E229F7B68
	for <caml-list@yquem.inria.fr>; Wed, 21 Feb 2007 20:36:03 +1100 (EST)
Date: Wed, 21 Feb 2007 20:36:03 +1100
From: Erik de Castro Lopo <mle+ocaml@mega-nerd.com>
To: caml-list@yquem.inria.fr
Subject: Combinatorics in a functional way
Message-Id: <20070221203603.e222647a.mle+ocaml@mega-nerd.com>
Organization: Erik Conspiracy Secret Labs
X-Mailer: Sylpheed version 2.3.0beta5 (GTK+ 2.8.20; i486-pc-linux-gnu)
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
X-Miltered: at concorde with ID 45DC1288.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)!
X-Spam: no; 0.00; ocaml:01 permutations:01 cheers:01 spyware:98 adware:98 lazy:02 functional:02 functional:02 ugly:03 let:03 let:03 erik:04 erik:04 coding:05 i'm:09 

Hi all,

I'm currently working on something where I need to to generate a
set of permutations that fit a set of rules. Currently I am doing
something like:

    let find_combi p0 p1 =
        let out = ref [] in
	for i0 = 1 to p0 do
            for i1 = 1 to p0 do
                for i2 = 1 to p0 do
                    for i3 = 1 to p1 do
                        for i4 = 1 to p1 do
                            for i5 = 1 to p1 do
                                for i6 = 1 to p1 do
                                    for i7 = 1 to p1 do
                                        if test_combi i0 i1 i2 i3 i4 i5 i6 i7 then
                                            lst := (i0, i1, i2, i3, i4, i5, i6, i7) :: lst
                                    done ;
                                done ;
                            done ;
                        done ;
                    done ;
                done ;
            done ;
        done ;
        !lst

This works, but I find it excessively ugly. It feels like I'm coding
in C again!

Can anyone come up with a cleaner, more functional way of solving 
problems like this? I'm thinking that something like lazy lists
might be a solution.

Any tips appreciated.

Cheers,
Erik
-- 
+-----------------------------------------------------------+
  Erik de Castro Lopo
+-----------------------------------------------------------+
Microsoft VISTA : Virus Infection Spyware Trojans and Adware!