functional provides Python users with numerous
tools common in functional programming, such as foldl, foldr, flip, as well
as mechanisms for partial function application and function composition.
functional also includes sane versions of the Python builtins map() and filter(),
written without the weird semantics of the builtin versions.
functional comes in two flavours: one is written in a combination of C and
Python, focusing on performance. The second is written in pure Python and
emphasises code readability and portability. The pure-Python variant is also
recommended if your setup does not allow compilation of third-party extension