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From: Benedikt Rosenau <Benedikt.Rosenau@dlr.de>
Message-Id: <200206171356.g5HDu5u19866@n05.sp.go.dlr.de>
Subject: [Caml-list] Memoizing (was: static variables...)
To: caml-list@inria.fr
Date: Mon, 17 Jun 2002 15:56:04 +0200 (DFT)
Cc: vanicat@labri.u-bordeaux.fr
In-Reply-To: <87k7oyreva.dlv@wanadoo.fr> from "Remi VANICAT" at Jun 17, 2002 01:19:21 AM
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Remi Vanicat wrote:

[...]

> let memoize f =
>   let stow = Hashtbl.create 20 in
>   fun x -> begin
>     if not (Hashtbl.mem stow x) then begin
>       try (let v = f x in Hashtbl.replace stow x (Val v))
>         with e -> Hashtbl.replace stow x (Exn e)
>      end;
>     match Hashtbl.find stow x with
>       | Val x -> x
>       | Exn e -> raise e
>   end

I tried to memoize the Ackermann function

# let rec ack m n =
    if m = 0 then n + 1
    else if n = 0 then ack (m - 1) 1
    else ack (m - 1) (ack m (n - 1))
val ack : int -> int -> int = <fun>
# let my_ack = memoize ack;;
val my_ack : int -> int -> int = <fun>


The type checker deals with the 'a being an (int -> int).
However, I noticed no speedup. So, I transformed the
Ackermann to the tupled version, ie "let ackermann (m, n)...",
but to no avail.

What is the mistake?

Regards,
   Benedikt
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