formatAsString.php

<?php

function formatAsString($data)
{
    if (is_array($data)) {
        $result = array();
        foreach ($data as $key => $value) {
            $result[] = sprintf('%s => %s', formatAsString($key), formatAsString($value));
        }

        return sprintf("[%s]", join(', ', $result));
    }

    if (is_bool($data)) {
        return $data ? 'true' : 'false';
    }

    return (string) $data;
}

var_dump(formatAsString('foo'));
var_dump(formatAsString(true));
var_dump(formatAsString(array(array('foo' => 'a', 'c', 'd' => false), 'b')));