Re: [caml] Closures and efficiency

From: Xavier Leroy (
Date: Fri Oct 29 1999 - 10:56:29 MET DST

Date: Fri, 29 Oct 1999 10:56:29 +0200
From: Xavier Leroy <>
To: Christopher Jeris <>,
Subject: Re: [caml] Closures and efficiency
In-Reply-To: <>; from Christopher Jeris on Tue, Oct 26, 1999 at 06:06:28PM -0400

> 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

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