day-5.py

# This problem was asked by Jane Street.

# cons(a, b) constructs a pair, and car(pair) and cdr(pair) returns the first and last element of that pair. For example, car(cons(3, 4)) returns 3, and cdr(cons(3, 4)) returns 4.

# Given this implementation of cons:

# def cons(a, b):
#     def pair(f):
#         return f(a, b)
#     return pair


# Implement car and cdr.

# Problem seems pretty straightforward at first sight

def cons(a, b):
    def pair(f):
        return f(a, b)
    return pair

def car(func):
    return func(lambda a,b: a)

def cdr(func):
    return func(lambda a,b: b)


print(car(cons(3, 4)))