From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: weis
Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id TAA06930 for caml-redistribution; Fri, 29 Oct 1999 19:21:21 +0200 (MET DST)
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id KAA11949 for <caml-list@pauillac.inria.fr>; Fri, 29 Oct 1999 10:56:51 +0200 (MET DST)
Received: from pauillac.inria.fr (pauillac.inria.fr [128.93.11.35])
	by concorde.inria.fr (8.8.7/8.8.7) with ESMTP id KAA09512;
	Fri, 29 Oct 1999 10:56:30 +0200 (MET DST)
Received: (from xleroy@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id KAA09378; Fri, 29 Oct 1999 10:56:29 +0200 (MET DST)
Message-ID: <19991029105629.43047@pauillac.inria.fr>
Date: Fri, 29 Oct 1999 10:56:29 +0200
From: Xavier Leroy <Xavier.Leroy@inria.fr>
To: Christopher Jeris <cjeris@math.mit.edu>, caml-list@inria.fr
Subject: Re: [caml] Closures and efficiency
References: <Pine.SUN.4.20.9910261748340.6977-100000@schauder.mit.edu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Mailer: Mutt 0.89.1
In-Reply-To: <Pine.SUN.4.20.9910261748340.6977-100000@schauder.mit.edu>; from Christopher Jeris on Tue, Oct 26, 1999 at 06:06:28PM -0400
Sender: weis

> Here's the nub of my question.  In a typical synth architecture there are
> very many parameters which take values 0..127.  If I had a function
> 
>   int_subrange_encoder: int -> int -> param_value -> bytestring
> 
> which took the bounds of a subrange and generated an encoder function for
> values of that subrange, and then in a voice-architecture description I
> had a list of very many records each of which contained an entry
> 
>   int_subrange_encoder 0 127
> 
> would I suddenly have six million little closures, or would the compiler
> do common-subexpression elimination on them ?

As of now, the compiler doesn't do any common subexpression
elimination.  Notice that CSE over function applications is hard,
because the compiler must make sure that the function has no side-effects.
E.g. assume your function int_subrange_encoder prints something after
receiving its first two arguments:

        let int_subrange_encoder lo hi =
          print_string "subrange_encoder was here!";
          fun param -> ...

Then, CSE would be incorrect.

An easy thing to do is to let-bind the partial applications that
occur frequently:

        let int_encoder = int_subrange_encoder 0 127

and then use "int_encoder" instead of "int_subrange_encoder 0 127"
in your descriptions.

Hope this helps,

- Xavier Leroy