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From: "SooHyoung Oh" <shoh@duonix.com>
To: "Caml-List" <caml-list@inria.fr>
Subject: [Caml-list] [q] on implementing of "memoization"
Date: Sat, 12 Apr 2003 10:20:32 +0900
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In testing "memoization" of fib function, it is OK on
    let rec fib = ... and memo_fib n = memoize fib n;;
but it makes the ERROR on
    let rec fib = ... and memo_fib = memoize fib;;

The error message is
      This kind of expression is not allowed as right-hand side of `let rec'

Why does this error occur?
I can't find good description on ocaml manual.

One more thing:
Do you have any idea about ** generic ** and good implementation of
memoization?

The source is
----------------------------------
let lookup key table = List.assoc key !table;;
let insert key value table = table := (key, value) :: !table;;

let table = ref [];;
let memoize f n =
    try
        lookup n table
    with
    | Not_found ->
        let result = f n in
        insert n result table;
        result
;;

let rec fib = function
    | 0 -> 0
    | 1 -> 1
    | n -> memo_fib (n-1) + memo_fib (n-2)
and memo_fib n = memoize fib n
;;
----------------------

Thanks a lot!

---
SooHyoung Oh

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