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[smlnj] View of /sml/trunk/src/MLRISC/library/cache.sml
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View of /sml/trunk/src/MLRISC/library/cache.sml

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Revision 651 - (download) (annotate)
Thu Jun 1 18:34:03 2000 UTC (19 years, 10 months ago) by monnier
File size: 537 byte(s)
bring revisions from the vendor branch to the trunk
(*
 * This is a simple cache datatype.
 *
 * -- Allen
 *) 

signature CACHE_REF =
sig

   type 'a cache 

   val cache : ('a -> 'b) -> 'a -> 'b cache
   val flush : 'a cache -> unit
   val !!    : 'a cache -> 'a

end

structure CacheRef :> CACHE_REF =
struct

   type 'a cache = 'a option ref * (unit -> 'a)

   fun cache f x = (ref NONE, fn _ => f x)

   fun flush (x as ref(SOME _),_) = x := NONE
     | flush (x,_) = ()

   fun !! (r as ref NONE,f)    = let val x = f() in r := SOME x; x end
     | !! (r as ref(SOME x),f) = x

end 


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