var newState = drawManuel( drawBackground( processInput(state))); This isn't how functional programming must work to be functional prog

var newState = drawManuel( drawBackground( processInput(state))); This isn't how functional programming must work to be functional programming. The point is always to write as much as possible in functional, preferably immutable style, if only it fits well. You can write a large portion of your program that way. The next sacrifice is to glue the functional calls together with more of a stateful approach, but preferably keep the mutable state more contained. For example, having a single function that handles the state, calls into the immutable functional code to do the heavy lifting, then sew everything together and ideally return something that is immutable and stateless. Like little bubbles of state where absolutely needed. For example, draw() calls in the above example can't be functional as drawing relies on side-effects. There's nothing to return from a drawing function, so those can't natively be chained into nested function calls. The final level is usually some hodge-podge state management at the very top level where it becomes unavoidable in order to keep things organised and beautiful. There's always some state, so you'll have to do it somewhere, but the more localized and minimized the better state management it is.