Functor A Functor is any data type that defines how fmap applies to it. Lists are functors too! Functions are Functors too. When you use fmap on a function, you're just doing function composition! Functors

str in Python2 and Python3 It turns out that the Python 2 str type doesn't hold a string; it holds a sequence of bytes. In the old ASCII world, a string was simply a sequence of bytes, so this distinction