使用生成器来生成一个平方数列表

function squares($start,$stop){
if($start > $stop){
for($i = $start; $i <= $stop; $i++){
yield $j = $i;
}
}else{
for($i = $stop; $i >= $start; $i--){
yield $i => $i *$i;
}
}

}

for(squares(3,15) as $n =>$square){
printf("%d squared is %d",$n, $square);
print "
";
}