type address = (string, int);

type mapper<T, U> = Closure<(T), U>;

type reducer<T, U> = Closure<(T, U), U>;

type filter<T> = Closure<(T), bool>;

function vec_filter<T>(
    vec<T> $vec,
    filter<T> $filter
): vec<T> {
    $result = vec[];
    foreach $vec as $item {
        if $filter($item) {
            $result[] = $item;
        }
    }

    return $result;
}

function vec_map<T, U>(
    vec<T> $vec,
    mapper<T, U> $mapper
): (vec<T>, vec<U>) {
    $result = vec[];
    foreach $vec as $item {
        $result[] = $mapper($item);
    }

    ($vec, $result)
}

function dict_filter<K, V>(
    dict<K, V> $dict,
    filter<V> $filter
): dict<K, V> {
    $result = dict[];
    foreach $dict as $key => $item {
        if $filter($item) {
            $result[$key] = $item;
        }
    }

    return $result;
}

function dict_map<K, V, U>(
    dict<K, V> $dict,
    mapper<V, U> $mapper
): (dict<K, V>, dict<K, U>) {
    $result = dict[];
    foreach $dict as $key => $item {
        $result[$key] = $mapper($item);
    }

    ($dict, $result)
}

function iterable_map_to_dict<K, V, U>(
    iterable<K, V> $iterable,
    mapper<V, U> $mapper
): (iterable<K, V>, dict<K, U>,) {
    $result = dict[];
    foreach $iterable as $key => $item {
        $result[$key] = $mapper($item);
    }

    ($iterable, $result)
}

function iterable_filter_to_dict<K, V>(
    iterable<K, V> $iterable,
    filter<V> $filter
): dict<K, V> {
    $result = dict[];
    foreach $iterable as $key => $item {
        if $filter($item) {
            $result[$key] = $item;
        }
    }

    return $result;
}