class Lazy:
__slots__ = ('thunk', 'result')
def __init__(self, thunk):
self.thunk = thunk
def force(self):
if self.thunk is not None:
self.result = self.thunk()
self.thunk = None
return self.result
def eager(lazy_list):
result = []
while True:
cell = lazy_list.force()
if cell is None:
return result
result.append(cell[0])
lazy_list = cell[1]
lazy_list = Lazy(lambda: (1, Lazy(lambda: (2, Lazy(lambda: (3, Lazy(lambda: None)))))))
print(eager(lazy_list))
print(eager(lazy_list))
print(eager(lazy_list))
