def test_first_is_lazy():
def once():
yield Just(42)
raise Exception
assert first(once()) == Just(42)
def test_first_wrap_just_only_if_not_already():
assert first([False, True], predicate=bool) == Just(True)
assert first([False, Just(True)], bool) != Just(Just(True))
assert first([False, Just(True)], bool) == Just(True)
def test_first_default():
assert first([Nothing, Nothing], default=Just(42)) == Just(42)
def test_first_predicate():
assert first([False, 0, 2, 1], predicate=bool) == Just(2)
assert first([False, 0, ''], predicate=bool) == Nothing
assert first(range(100), predicate=lambda x: x > 50) == Just(51)
assert first(range(100), predicate=lambda x: x > 100) == Nothing
def test_first():
assert first([Nothing, Just(42)]) == Just(42)
assert first([Just(42), Just(43)]) == Just(42)
assert first([Nothing, Nothing]) == Nothing
assert first([]) == Nothing