Sure, we can always translate away state and pass it explicitly. Some people find some algorithms can be more naturally expressed using state. (And "some peopl

Sure, we can always translate away state and pass it explicitly. Some people find some algorithms can be more naturally expressed using state. (And "some people" is a polite way of saying "alot".) The question of whether state can always be replaced by pure functions without loss of asymptotic complexity is open as of April 2016. All I wanted to point out is that there is no need of becoming a functional Taliban: if state is kept local, that's usually fine. when you get to more complicated things Yes. Then don't use it. My rule of thumb is: definition and all uses of state should be visible to the programmer without scrolling.