#!/usr/bin/env python3

def square(x: int) -> int:
    return x ** 2

# Main function
def main() -> None:
    """
    lambda: a one-liner anonymous function. in its simplest form, it just a function.
    for example, the following can be rewritten with a add_1 function which returns x + 1
    """
    add_1 = lambda x: x + 1
    result = add_1(1)
    print(result)

    """
    map function: apply a function to every element in an iterable
    returns a map object which can then be casted to a list
    """
    numbers = range(1,10)
    # square is the function and numbers is the iterable where elements will be sent from
    results = list(map(square, numbers))
    print(results)

    """
    implement the same map function with lambda
    """
    results2 = list(map(lambda x: x ** 2, numbers))
    print(results2)

    """
    filter function: apply function to every element. if true, keep the element. if false, reject it
    """
    even_numbers = list(filter(lambda x: x % 2 == 0, numbers))
    print(even_numbers)

# Call main function
if __name__ == '__main__':
    main()