extend map {
    function containsKey(key) {
        return this.keys.contains(key);
    }

    function containsValue(value) {
        return this.values.contains(value);
    }

    function contains(key, value) {
        return (this as (v, k) ^ v % (k == key) and (v == value)).size > 0;
    }

    function isEmpty() {
        return this.size == 0;
    }

    function isNotEmpty() {
        return not this.isEmpty();
    }

    function getOrDefault(key, default) {
        if(this.containsKey(key)) {
            return this.get(key);
        }

        return default;
    }
}