PHP里的闭包函数

<?php
$f = function($s)
{
  echo $s;  
}; //这个分号不能丢，否则会报错
$f(‘HELLO‘);

<?php
function test()
{
  $f = function ($s)
 {
   echo $s;
 };
 $f(‘HELLO‘);
}
test();

<?php
function test(){
    $f = function($s)
    {
        echo $s;  
    }; 
    return $f;     
}
$r = test();
$r(‘HELLO‘)

<?php
function test(){
   $a = 1;
   $b = 2;
   $f = function() use($a, $b){
       echo $a;
       echo $b;
   }
}
test();