Memoizing pure functions

memoization.fs

open System.Collections.Generic
let memoize (f : 'a -> 'b) =
let dict = new Dictionary<'a, 'b>()
let memoizedFunc (input : 'a) =
match dict.TryGetValue(input) with
| true, x -> x
| false, _ ->
// Evaluate and add to lookup table
let answer = f input
dict.Add(input, answer)
answer
// Return our memoized version of f dict is captured in the closure
memoizedFunc