From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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=AWL autolearn=disabled version=3.1.3 X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from discorde.inria.fr (discorde.inria.fr [192.93.2.38]) by yquem.inria.fr (Postfix) with ESMTP id ADE60BC6B for ; Thu, 28 Jun 2007 13:37:51 +0200 (CEST) Received: from ptb-relay03.plus.net (ptb-relay03.plus.net [212.159.14.214]) by discorde.inria.fr (8.13.6/8.13.6) with ESMTP id l5SBbnxg014009 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=NO) for ; Thu, 28 Jun 2007 13:37:51 +0200 Received: from [80.229.56.224] (helo=beast.local) by ptb-relay03.plus.net with esmtp (Exim) id 1I3sJm-00045M-P2 for caml-list@yquem.inria.fr; Thu, 28 Jun 2007 12:37:46 +0100 From: Jon Harrop Organization: Flying Frog Consultancy Ltd. To: caml-list@yquem.inria.fr Subject: Re: [Caml-list] The Implicit Accumulator: a design pattern using optional arguments Date: Thu, 28 Jun 2007 12:32:01 +0100 User-Agent: KMail/1.9.7 References: <200706271314.35134.jon@ffconsultancy.com> <200706271653.27116.jon@ffconsultancy.com> <4683950E.3060609@functionality.de> In-Reply-To: <4683950E.3060609@functionality.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200706281232.01643.jon@ffconsultancy.com> X-Miltered: at discorde with ID 46839D8D.004 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)! X-Spam: no; 0.00; mutation:01 ocaml:01 ocaml:01 frog:98 wrote:01 wrote:01 abstract:01 rec:01 rec:01 clearer:01 caml-list:01 lisp:01 nums:01 nums:01 linear:02 On Thursday 28 June 2007 12:01:34 Thomas Fischbacher wrote: > Jon Harrop wrote: > > I think Thomas is referring to continuation passing style (CPS). That > > isn't an optimization though (it slows things down) but it does let you > > abstract away mutation. However, it is not entirely safe in the absence > > of linear types. > > Which one do you prefer? > > let sum_nums n = > let rec work sum todo = > if todo=0 then sum > else work (sum+todo) (todo-1) > in work 0 n > ;; > > let sum_nums2 n = > let rec work (sum,todo) = > if todo=0 then sum > else work ((sum+todo),(todo-1)) > in work (0,n) > ;; > > Certainly the first one, right? I would write: let rec work sum = function | 0 -> sum | todo -> work (sum + todo) (todo - 1) let sum_nums n = work 0 n because it is shorter, clearer, 65% faster and it is idiomatic ML rather than idiomatic Lisp. -- Dr Jon D Harrop, Flying Frog Consultancy Ltd. The OCaml Journal http://www.ffconsultancy.com/products/ocaml_journal/?e