From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from mail1-relais-roc.national.inria.fr (mail1-relais-roc.national.inria.fr [192.134.164.82]) by yquem.inria.fr (Postfix) with ESMTP id 6D876BC37 for ; Fri, 16 Oct 2009 17:15:08 +0200 (CEST) X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AqMCANIq2ErRVd+smGdsb2JhbACPVYsBPwEBAQEJCQwHE64thl2IZQEDAwWEKwSBW4Upggc X-IronPort-AV: E=Sophos;i="4.44,573,1249250400"; d="scan'208";a="38402107" Received: from mail-iw0-f172.google.com ([209.85.223.172]) by mail1-smtp-roc.national.inria.fr with ESMTP; 16 Oct 2009 17:15:07 +0200 Received: by iwn2 with SMTP id 2so1146088iwn.1 for ; Fri, 16 Oct 2009 08:15:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to:cc :content-type:content-transfer-encoding; bh=A2XqYG/V4eRt/HHB4OXO+H2kLY7GmbRziihXKyysl5I=; b=mCG4VrvpR+HKuimgzXylDbcToRYlapBLcRWvnuQviCmGYPoIS4HjbtXnBtdTdoEvNx 3l4kaYJSTQy2yfY2DZXyhw3X2BZelHnPr7aiGRiJj62ES4FwJPsIBaLsvqgcj0hILIRc dteBDfAS2SYKkAo6kvtetOG6/M4d+FsiwkXJo= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=gfsMJG8ztkF6ksugT3LTpiG2BUbflkvPCHw7dnnGD8GDEVD2h3f3bXFSxrxJiROEG4 htgCJ+fCww+Za/EnnBrlbFSTmvdwgaI06INZ9iv9EFPFbp5RUnwT9Nh3bck3uw41uRwJ OM99FEJMRwIdRj0b/32exAXjbIDIx/xQ7aUOQ= MIME-Version: 1.0 Sender: till.varoquaux@gmail.com Received: by 10.231.123.216 with SMTP id q24mr4999207ibr.43.1255706107005; Fri, 16 Oct 2009 08:15:07 -0700 (PDT) In-Reply-To: References: Date: Fri, 16 Oct 2009 11:15:06 -0400 X-Google-Sender-Auth: 81eee313f8743183 Message-ID: <9d3ec8300910160815n76a47727h7f5bf13623f18125@mail.gmail.com> Subject: Re: [Caml-list] How to add () to function parameters From: Till Varoquaux To: Till Crueger Cc: caml-list@yquem.inria.fr Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam: no; 0.00; val:01 unparsing:01 danvy:01 abstracting:01 printf:01 scanf:01 brics:01 ocaml:01 node:01 beginner's:01 ocaml:01 bug:01 countless:98 2009:98 blog:98 Well I can basically see two solutions (plus countless complications that I won't go into.) We want to define a function val cps3: f:('a -> 'b -> 'c -> 'd) -> ('d -> 'e) -> 'a -> 'b -> 'c -> 'e = =3D that takes a three argument function a returns the same function in CPS sty= le. The functional unparsing/danvy way [1]: > let (++) f g =3D fun x -> f (g x) > let i k f arg =3D k (f arg) > let cps ty ~f k =3D ty k f > let cps3 ~f =3D cps (i++i++i) ~f brute force style: > let e acc ~f cont =3D acc cont f > let i =3D fun acc g -> g (fun cont v arg -> acc cont (v arg)) > let cps =3D fun z -> > let acc =3D (fun cont x -> cont x) in > z acc > let cps3 ~f =3D cps i i i e ~f The first style is an acquired taste quite the same way that monad are. With some getting use to and abstracting your types in a sensible way you can enclose things quite nicely and define elegant printf/scanf kind of functions. I strongly discourage you to use the second style. It is a very reworked mlton.fold [2] style solution. mlton's fold is a lot more esoteric and leads to types that I have never been able to abstract properly. Till [1] http://www.brics.dk/RS/98/12/ [2] http://mlton.org/Fold On Wed, Oct 14, 2009 at 6:44 AM, Till Crueger wrote: > Hi, > > I am looking for a way to add a unit parameter to a function that takes a= n > arbitrary number of parameters. If the number of parameters is known this= is > fairly easy and I can just do: > > let lift1 f a =3D > =C2=A0 fun () -> > =C2=A0 =C2=A0 =C2=A0f a;; > > let lift2 f a b =3D > =C2=A0 fun () -> > =C2=A0 =C2=A0 f a b;; > > (all these create one closure per lifting) > etc... > > However it is a bit of a hassle to have to code each of these lifts... So > what I am looking for is a way to extend this pattern to all numbers. So = far > I got to the point that I can do the following: > > let lift_once f a =3D > =C2=A0 fun () -> > =C2=A0 =C2=A0 =C2=A0f a;; > > let lift_more f a =3D > =C2=A0 fun () -> > =C2=A0 =C2=A0 =C2=A0f () a;; > > So for a function f taking two parameters a and b I can do > > lift_more (lift_once f a) b > (two closures created) > > and for a function taking the parameters a, b and c I can do > > lift_more (lift_more (lift_once f a) b) c > (three closures created) > > to get the lifted functions. > > However this solution gets quite ugly with all the parentheses. Also ther= e > are a lot of closures being produced and evaluated for any single lifting= . I > had a look at the Jane Street blog post about variable argument functions > (http://ocaml.janestcapital.com/?q=3Dnode/22), which seems to do similar > things. However I have never been really good with CPS, so I don't know i= f > those techniques can be applied to this problem. > > Is there any way to do this, which does not get this ugly. Also the > resulting lifted function should not contain too many closures. > > Thanks for your help, > =C2=A0 Till > > _______________________________________________ > Caml-list mailing list. Subscription management: > http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list > Archives: http://caml.inria.fr > Beginner's list: http://groups.yahoo.com/group/ocaml_beginners > Bug reports: http://caml.inria.fr/bin/caml-bugs >