Flatten lists
Created on May 19, 2020 by Julien Palard
Write a flatten
function, which given a list of lists (of any depth)
returns a flattened version of it.
Example
>>> flatten([[1], 2, [[3, 4], 5], [[[]]], [[[6]]], 7, 8, []])
[1, 2, 3, 4, 5, 6, 7, 8]