008+ Fatal error: Uncaught TypeError: Argument 2 passed to array_walk_recursive() must be callable, string given in %s/array_walk_recursive_variation8.php:25
009+ Stack trace:
010+ #0 %s/array_walk_recursive_variation8.php(25): array_walk_recursive(Array, 'echo')
008- Warning: array_walk_recursive() expects parameter 2 to be a valid callback, function 'echo' not found or invalid function name in %s on line %d
009- NULL
010- Done
011+ #1 {main}
012+ thrown in %s/array_walk_recursive_variation8.php on line 25