斐波纳契数列通常做法是用递归实现，当然还有其它的方法。这里现学现卖，用PHP的迭代器来实现一个斐波纳契数列，几乎没有什么难度，只是把类里的next()方法重写了一次。注释已经写到代码中，也是相当好理解的。

<?php
/*
*@author nicesunboy@gmail.com
*/
class Fibonacci implements Iterator { 
    private $previous = 1; 
    private $current = 0; 
    private $key = 0; 
    
    public function current() { 
        return $this->current; 
    } 
    
    public function key() { 
        return $this->key; 
    } 
    
    public function next() { 
		// 关键在这里
		// 将当前值保存到  $newprevious
        $newprevious = $this->current; 
		// 将上一个值与当前值的和赋给当前值
        $this->current += $this->previous; 
		// 前一个当前值赋给上一个值
        $this->previous = $newprevious; 
        $this->key++; 
    } 
    
    public function rewind() { 
        $this->previous = 1; 
        $this->current = 0; 
        $this->key = 0; 
    } 
    
    public function valid() { 
        return true; 
    } 
} 

$seq = new Fibonacci; 
$i = 0; 
foreach ($seq as $f) { 
    echo "$f "; 
    if ($i++ === 15) break; 
} 
?>

程序运行结果：

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610