Some people claim that one is often able to make programs with a mostly functional core; in which case most of the code is purely functional. Actually, I think

Some people claim that one is often able to make programs with a mostly functional core; in which case most of the code is purely functional. Actually, I think that is the best way to do most things. Mutable state should be documented and sequestered. Perhaps what I consider "pure functional programming" (i.e. a project with all-functional code, except perhaps an I/O layer) is unreasonably purist.