RE: [Caml-list] partial eval question

["Ben Kavanagh" <kavabean@lmi.net>]

Walid, 

Thanks for your response. I was aware of MetaOCaml's ability to stage
this computation and I have downloaded/run many of your benchmarks. My
question was if anyone had an implementation where normal partial
application (normal in ML's syntax) led to partial evaluation. It turns
out that there was an implementation of this, namely Mark Leone/Peter
Lee's Fabius compiler, which, unfortunately, has never been made
available publicly. 

http://portal.acm.org/citation.cfm?id=231407&dl=ACM&coll=portal&CFID=111
11111&CFTOKEN=2222222
http://portal.acm.org/citation.cfm?id=289144&dl=ACM&coll=portal

I concur that such an undiscriminating approach to partial evaluation in
a program is not ideal, a point you touch on in a later mail to the Caml
list.

It does seem, though, that a useful syntax shortcut that made this
direct partial-application -> partial-eval mapping available in the
manner of Lee/Leone could be useful in MetaOCaml. 

Do you agree?

Ben




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-----Original Message-----
From: Walid Taha [mailto:taha@cs.rice.edu] 
Sent: Wednesday, February 04, 2004 2:51 AM
To: Ben Kavanagh
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] partial eval question


Hi Ben,

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

----- 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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-- 





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