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[caml] Closures and efficiency
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Date: -- (:)
From: Xavier Leroy <Xavier.Leroy@i...>
Subject: Re: [caml] Closures and efficiency
> 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