. * * To disable strict typing, comment out the directive below. */ declare(strict_types=1); class ListOps { public function append(array $list1, array $list2): array { $list = $list1; foreach ($list2 as $item) { $list[] = $item; } return $list; } public function concat(array $list1, array ...$listn): array { $res = $list1; foreach ($listn as $list) { foreach ($list as $item) { $res[] = $item; } } return $res; } /** * @param callable(mixed $item): bool $predicate */ public function filter(callable $predicate, array $list): array { return array_values(array_filter($list, $predicate)); } public function length(array $list): int { return count($list); } /** * @param callable(mixed $item): mixed $function */ public function map(callable $function, array $list): array { return array_map($function, $list); } /** * @param callable(mixed $accumulator, mixed $item): mixed $function */ public function foldl(callable $function, array $list, $accumulator) { return array_reduce($list, $function, $accumulator); } /** * @param callable(mixed $accumulator, mixed $item): mixed $function */ public function foldr(callable $function, array $list, $accumulator) { return array_reduce(array_reverse($list), $function, $accumulator); } public function reverse(array $list): array { return array_reverse($list); } }