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Date: Mon, 27 Oct 2003 08:14:53 +0100
From: Damien <Damien.Pous@ens-lyon.fr>
Cc: <caml-list@inria.fr>
Subject: Re: [Caml-list] partial eval question
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On Mon, 27 Oct 2003 01:41:49 -0000 Ben Kavanagh wrote:

> Say I have a function such as pow defined as
> 
> let pow n x = 
>     let rec pow_iter (n1, x1, p1) = 
>         if (n1 = 0) then p1 
>         else if (n1 mod 2 = 0) 
> 		 then pow_iter(n1/2, x1*x1, p1) 
>              else pow_iter(n1-1, x1, p1*x1)
>     in pow_iter(n, x, 1);;
> 
> and I say 
> 
> let pow2 = pow 2
> 
> Are there any ML implementations that would automatically perform
> partial evaluation to create pow2 instead of using closures, possibly
> unfolding the pow_iter call? Would Caml ever have this capability?

Multi-Stage Programming is your friend...
<http://www.cs.rice.edu/~taha/MSP/>

There are two ML implementations :
Ocaml : MetaOCaml <http://www.cs.rice.edu/~taha/MetaOCaml/>
SML : MetaML <http://www.cse.ogi.edu/PacSoft/projects/metaml/>


let rec pow n = .< 
	.~(match n with
		| 1 -> .< fun x -> x >.
		| n -> .< fun x -> x * .~(pow (n-1)) x>.
	)
>.

(pow 3) get reduced into .<fun x -> x*x*x>.


Damien

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