How to define a function in functional programming?

Question

I am trying to learn Functional Programming, and I am doing so with Python. An exercise I am trying do is to make a function that returns true if a number is even.

def evenOrOdd(x):
return lambda x: x%2 == 0

print(evenOrOdd(1))
print(evenOrOdd(2))
print(evenOrOdd(3))
print(evenOrOdd(4))
<function evenOrOdd.<locals>.<lambda> at 0x7f7a9a145670>
<function evenOrOdd.<locals>.<lambda> at 0x7f7a9a145670>
<function evenOrOdd.<locals>.<lambda> at 0x7f7a9a145670>
<function evenOrOdd.<locals>.<lambda> at 0x7f7a9a145670>

This is what I have at the moment, but as you see, it is not returning a boolean.

Answer 1

You either do this: (declaring a normal function)

def evenOrOdd(x):
    return x%2 == 0

or this: (declaring a function using a lambda)

evenOrOdd = lambda x: x%2 == 0

This

def evenOrOdd(x):
    return lambda x: x%2 == 0

means you are returning a lambda function from the function evenOrOdd. In this case the variable x makes no actual difference, since the lambda redefines it. You could call it like so:

evenOrOdd(999)(2) #999 could be anything