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[Caml-list] partial eval question
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 Date: 2004-02-04 (02:51) From: Walid Taha Subject: Re: [Caml-list] partial eval question
```
Hi Ben,

Below is a MetaOCaml (www.metaocaml.org) program that does what you were

----- begin ben.ml

Trx.init_times (* Initialize MetaOCaml timer library *)

(* Here's Ben's original code *)

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);;

let pow2 = pow 2

(* Here's a staged version of Ben's code *)

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>.);;

let pow2 = pow' 2

(* Here's some code to get some timings *)

let unstagedRunning =
Trx.timenew "unstaged running"(fun () -> pow 5 3)

let stage1Running =
Trx.timenew "stage 1 running" (fun () -> .<fun x-> .~(pow' 5 .<x>.)>.)

let compiling = Trx.timenew "compiling" (fun () -> .! stage1Running)

let stage2Running = Trx.timenew "stage 2 running" (fun () -> (compiling
3))

let baseline = Trx.timenew "baseline" (fun () -> ())

(* Print all the timings *)

let _ = Trx.print_times ()

(* Outpout of timer:
__ unstaged running ______ 2097152x avg= 7.929525E-04 msec
__ stage 1 running ________ 262144x avg= 7.248323E-03 msec
__ compiling ________________ 8192x avg= 2.320860E-01 msec
__ stage 2 running ______ 16777216x avg= 1.123075E-04 msec
__ baseline _____________ 33554432x avg= 3.921819E-05 msec
*)

--- end ben.ml

Walid.

On Mon, 27 Oct 2003, 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?
|
|Ben
|
|
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