reverse.py

cons = lambda a, b: lambda x: a if x else b

Y = lambda f: (lambda x: f(lambda y: x(x)(y)))(lambda x: f(lambda y: x(x)(y)))

pretty = lambda l: "(" + Y(lambda f: lambda l: cons(lambda: str(l(1)) + cons(" ", "")(l(0)) + f(l(0)), lambda: ")")(l)())(l)

reverse = Y(lambda f: lambda k: lambda l: cons(lambda: f(cons(l(1), k))(l(0)), lambda: k)(l)())(None)

assert pretty(cons(1, cons(2, cons(3, None)))) == "(1 2 3)"
assert pretty(reverse(cons(1, cons(2, cons(3, None))))) == "(3 2 1)"