play.swift

// Playground - noun: a place where people can play

import Cocoa


func main() {

  func _fib(x: Int, y: Int, i: Int) -> Int {

    if i == 1 || i == 0 {
      return x + y
    } else {
      return _fib(y, x + y, i - 1)
    }
  }

  func fib(n: Int) -> Int {

    if n == 0 {
      return 0
    }
    return _fib(0, 1, n)
  }

  fib(10)

}

main()