def parse_non_empty(self, start, level):
grammars = Cursor(self.grammars)
result = False
end = start
while grammars.not_empty() and not result:
(result, end) = grammars.head().parse(start, level + 1)
if not result:
grammars = grammars.tail()
return (result, end)
def test_traversal(self):
items = []
cursor = Cursor([1, 2, 3])
items.append(cursor.head())
tail1 = cursor.tail()
items.append(tail1.head())
tail2 = tail1.tail()
items.append(tail2.head())
tail3 = tail2.tail()
self.assertEqual(items, [1, 2, 3])
self.assertTrue(tail3.empty())
