get_defined_functions

<?php
function myrow($id, $data) {
    return "<tr><th>$id</th><td>$data</td></tr>\n";
}

$arr = get_defined_functions();

print_r($arr);
?>

Array
(
    [internal] => Array
        (
            [0] => zend_version
            [1] => func_num_args
            [2] => func_get_arg
            [3] => func_get_args
            [4] => strlen
            [5] => strcmp
            [6] => strncmp
            ...
            [750] => bcscale
            [751] => bccomp
        )

    [user] => Array
        (
            [0] => myrow
        )

)