5_JaneStreet_functional_programming.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.
'''

def my_tuple(a,b):
    return (a,b)

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

def cdr(pair):
    _,b = pair(my_tuple)
    return b

def car(pair):
    a,_ = pair(my_tuple)
    return a

if __name__ == '__main__':
    print(cdr(cons(3,4)))
    print(car(cons(3,4)))