Fibonacci

fibonacci.py

# coding: utf-8

from itertools import takewhile

def fib():
  a = 1
  b = 1
  while True:
    yield a
    tmp = b
    b = a + b
    a = tmp

fib_stream = fib()

for x in takewhile(lambda n: n < 4000, fib_stream):
  print(x)

Fibonacci.scala

object Main extends App{
  // 真面目に書いた正格評価の fib seq
  fib(10).foreach { println }
  
  def fib(n: Int): Seq[Int] = {
    assert(n > 0)
    
    def rec(n: Int, a: Int, b: Int, seq: Seq[Int]): Seq[Int] = (n <= 1) match {
      case true => seq
      case false => rec(n - 1, b, a + b, seq :+ b)
    }
    
    rec(n, 1, 1, Seq(1))
  }
  
  // Stream 調べたらソッコーで出てきてしまった fib stream
  val fibStream: Stream[Int] = 1 #:: fibStream.scanLeft(1){ _ + _ }
  
  fibStream.takeWhile{ _ < 40000}.foreach{ println }
}