php5:

<?php

function check_error($errno) {
    
    $error = array(
        'some error',
        'some other error',
        'third error'
    );

    return $error[$errno];

}

$errno = 2;

if(isset(check_error($errno))) {
    var_dump($_SERVER);
}

?>

result:

Fatal error: Can't use function return value in write context in g:\workspace\WEB\www\arr.php on line 17

php4: 
same code
nothing dumped

any comments?