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fun find cache x =
case (List.find (fn (y,_) => x = y) (!cache)) of
NONE => NONE
| SOME (_,r) => SOME r
fun remove cache x =
cache := (List.filter (fn (y,_) => not (x = y)) (!cache))
fun insert cache (x,r) =
cache := (x,r)::(!cache)
val cache = ref []
fun lookup (x : int) =
case find cache x of
SOME r => (case MLton.Weak.get r of
SOME r' => r'
| NONE => (remove cache x; lookup x))
| NONE => let val res = x + 1
val wres = MLton.Weak.new res
in insert cache (x, wres);
res
end
val _ = List.app (fn x => print (concat [Int.toString (lookup x), "\n"])) [5,4,3,2,1]
|
