10-Calculating-With-Functions.md

Calculating with Functions

This time we want to write calculations using functions and get the results. Let's have a look at some examples:

seven(times(five())) # must return 35
four(plus(nine())) # must return 13
eight(minus(three())) # must return 5
six(divided_by(two())) # must return 3

Requirements:

• There must be a function for each number from 0 ("zero") to 9 ("nine")
• There must be a function for each of the following mathematical operations: plus, minus, times, dividedBy (divided_by in Ruby and Python)
• Each calculation consist of exactly one operation and two numbers
• The most outer function represents the left operand, the most inner function represents the right operand
• Division should be integer division. For example, this should return 2, not 2.666666...: eight(divided_by(three()))

Solution

def zero(f=None): 
    if f is None: 
        return 0 
    else: 
        return f(0) 
def one(f=None): 
    if f is None: 
        return 1 
    else: 
        return f(1) 
def two(f=None): 
    if f is None: 
        return 2 
    else: 
        return f(2) 
def three(f=None): 
    if f is None: 
        return 3 
    else: 
        return f(3) 
def four(f=None): 
    if f is None: 
        return 4 
    else: 
        return f(4) 
def five(f=None): 
    if f is None: 
        return 5 
    else: 
        return f(5) 
def six(f=None): 
    if f is None: 
        return 6 
    else: 
        return f(6) 
def seven(f=None): 
    if f is None: 
        return 7 
    else: 
        return f(7) 
def eight(f=None): 
    if f is None: 
        return 8 
    else: 
        return f(8) 
def nine(f=None): 
    if f is None: 
        return 9 
    else: 
        return f(9) 

def plus(num): 
    return lambda x: x + num
def minus(num): 
    return lambda x: x - num
def times(num): 
    return lambda x: x * num
def divided_by(num): 
    return lambda x: int(x / num)