Memoize

memoize.swift

func memoize<T: Hashable, U>(work: @escaping (T)->U) -> (T)->U {
    var memo = Dictionary<T, U>()
    
    return { x in
        if let q = memo[x] { return q }
        let r = work(x)
        memo[x] = r
        return r
    }
}

// Recursion supporting version
func memoize<T: Hashable, U>(work: @escaping ((T)->U, T) -> U) -> (T)->U {
    var memo = Dictionary<T, U>()
    
    func wrap(x: T)->U {
        if let q = memo[x] { return q }
        let r = work(wrap, x)
        memo[x] = r
        return r
    }
    
    return wrap
}