Simple F# memoization

memoization_simple.fs

open System.Collections.Generic

// A simple function with some built in delay
// val square : int -> int
let square x = 
    System.Threading.Thread.Sleep(x * 1000)
    x * x

// A generic memoization function that takes a function with one parameter
// val memoization : ('a -> 'b) -> ('a -> 'b) when 'a : equality
let memoization (f: 'a -> 'b) =
    // Storage for the calculated result
    let cache = new Dictionary<_, _>()

    // Check if it's in the cache or not
    (fun x ->
        match cache.TryGetValue(x) with
        | true, cachedValue -> cachedValue
        | _ -> 
            let result = f x
            cache.Add(x, result)
            result)

// Try the memoization function
let memoSquare = memoization square

// Run it in the F# interactive with: #time;;
memoSquare 3
// and one more time
memoSquare 3