List out of lambda, Python versions

lol.py

empty_list = None
 
def prepend(el, lst):
    def func(selector):
        return selector(el, lst)
    return func
 
def head(lst):
    def selector(h, t):
        return h
    return lst(selector)
 
def tail(lst):
    def selector(h, t):
        return t
    return lst(selector)
    
def is_empty(lst):
    return lst is empty_list

a = prepend("a", prepend("b", empty_list))
assert("a" == head(a))
assert("b" == head(tail(a)))
assert(tail(tail(a))==empty_list)
assert(not is_empty(a))
assert(is_empty(empty_list))

lol2.py

empty_list = None

def prepend(el, lst):
    return lambda selector: selector(el, lst)

def head(lst):
    return lst(lambda h, t: h)

def tail(lst):
    return lst(lambda h, t: t)

def is_empty(lst):
    return (lst == empty_list)

a = prepend("a", prepend("b", empty_list))
assert("a" == head(a))
assert("b" == head(tail(a)))
assert(tail(tail(a))==empty_list)
assert(not is_empty(a))
assert(is_empty(empty_list))

lol3.py

empty_list = None
prepend = lambda el, list: lambda selector: selector(el, list)
head = lambda list: list(lambda h, t: h)
tail = lambda list: list(lambda h, t: t)
is_empty = lambda list: list is empty_list

a = prepend("a", prepend("b", empty_list))
assert("a" == head(a))
assert("b" == head(tail(a)))
assert(tail(tail(a))==empty_list)
assert(not is_empty(a))
assert(is_empty(empty_list))

lol4.py

class List(object):
    def __init__(self, list=None):
        self.list = list

    def prepend(self, el):
        return List(lambda selector: selector(el, self.list))

    def head(self):
        return self.list(lambda h, t: h)

    def tail(self):
        return List(self.list(lambda h, t: t))

    def is_empty(self):
        return not self.list

a = List().prepend("b").prepend("a")
assert("a" == a.head())
assert("b" == a.tail().head())
assert(a.tail().tail().is_empty())
assert(not a.is_empty())
assert(List().is_empty())

lol5.py

class List(object):
    def __init__(self, list=None):
        self.prepend = lambda el: List(lambda selector: selector(el, list))
        self.head = lambda: list(lambda h, t: h)
        self.tail = lambda: List(list(lambda h, t: t))
        self.is_empty = lambda: not list

a = List().prepend("b").prepend("a")
assert("a" == a.head())
assert("b" == a.tail().head())
assert(a.tail().tail().is_empty())
assert(not a.is_empty())
assert(List().is_empty())