gistfile1.swift

public func memoize<T: Hashable, U>(body: ((T) -> U, T) -> U) -> (T) -> U {
    var memo = Dictionary<T, U>()
    var result: ((T) -> U)!
    result = { x in
        if let q = memo[x] {
            return q
        }
        let r = body(result, x)
        memo[x] = r
        return r
    }
    return result
}