def __repr__(self):
curr = self
top = []
while not Symbol.isNIL(curr):
top.append(curr.car)
curr = curr.cdr
return '(' + ' '.join(repr(x) for x in top) + ')'
def __init__(self, car, cdr):
assert car is not None
assert cdr is not None
assert isinstance(car, Cons) or isinstance(car, Symbol)
assert isinstance(cdr, Cons) or Symbol.isNIL(cdr)
self.car = car
self.cdr = cdr
