memoize

// JavaScript
function memoize(fn) {
  var memo = {}
  return function(x) {
    return memo[x] || (memo[x] = fn(x))
  }
}

// Swift
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
}