/**
  * @dataProvider provideData
  */
 public function test_it_should_work_with_maybe($list, $expected)
 {
     $addSingleDigit = function ($acc, $i) {
         return $i > 9 ? m\nothing() : m\just($acc + $i);
     };
     $this->assertEquals($expected, f\foldM($addSingleDigit, 0, $list)->extract());
 }
 /**
  * @dataProvider provideData
  */
 public function test_it_should_extract_elements_which_exists_alternative_solution($data)
 {
     // $get :: String a -> Maybe [b] -> Maybe b
     $get = function ($key) {
         return f\bind(function ($array) use($key) {
             return isset($array[$key]) ? m\just($array[$key]) : m\nothing();
         });
     };
     $result = Listt::of($data)->map(Maybe\maybeNull)->bind($get('meta'))->bind($get('images'))->bind($get(0));
     $this->assertEquals(Listt::of([m\just('//first.jpg'), m\just('//third.jpg'), m\nothing()]), $result);
 }
 public function get($key)
 {
     return array_key_exists($key, $this->data) ? Maybe\just($this->data[$key]) : Maybe\nothing();
 }
 public function test_it_traverse_just()
 {
     $list = Listt::of([2, 4]);
     $result = f\traverse('example\\value_is', $list);
     $this->assertEquals(m\just([2, 4]), $result);
 }