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[smlnj] View of /sml/trunk/src/cm/util/memoize.sml
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View of /sml/trunk/src/cm/util/memoize.sml

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Revision 494 - (download) (annotate)
Tue Nov 30 09:07:21 1999 UTC (22 years, 8 months ago) by blume
File size: 785 byte(s)
memoize put into its own module
 * Simple memoization.
 * (C) 1999 Lucent Technologies, Bell Laboratories
 * Author: Matthias Blume (blume@kurims.kyoto-u.ac.jp)
structure Memoize :> sig
    (* If g is the result of (memoize f), then calling g the first time
     * will result in f being called with the same argument.
     * Any subsequent call to g simply returns the result that was
     * computed during the first call.  Thus, f will be called at most
     * once on g's behalf. *)
    val memoize : ('a -> 'b) -> ('a -> 'b)
end = struct
    fun memoize f = let
	val cache = ref (fn _ => raise Fail "Memoize.memoize: uninitialized")
	fun first_time x = let
	    val v = f x
	    fun later_on _ = v
	    cache := later_on;
	cache := first_time;
	(fn x => !cache x)

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