In the following code the callback function passed to wrap_map can't see the argument in the outer function, why? (see code comment for detail)
public static function wrap_implode($ar, $wrap, $delim){
echo "wrap is $wrap"; //wrap is ok
$res = array_map(function($val){
echo "wrap is $wrap"; //wrap is not set here!
return $wrap. $val . $wrap;
}, $ar);
return implode($delim, $res);
}
