public function testMapFilter() { $numbers = [1, 2, 3, 4]; $inc = function ($x) { return $x + 1; }; $isEven = function ($x) { return $x % 2 === 0; }; $xf = t::comp(t::map($inc), t::filter($isEven)); $result = t::into([], $xf, $numbers); $this->assertEquals([2, 4], $result); }