Is there a common technique to handle state (in general) in a functional programming language? There are solutions in every (functional) programming language to handle global state, but I want to avoid this as far as I could.
All state in a pure functional manner are function parameters. So I need to put the whole game state (a gigantic hashmap with the world, players, positions, score, assets, enemies, …)) as a parameter to all functions which wants to manipulate the world on a given input or trigger. The function itself picks the relevant information from the gamestate blob, do something with it, manipulate the gamestate and return the gamestate. But this looks like a poor mans solution for the problem. If I put the whole gamestate into all functions, there is no benefit for me in contrast to global variables or the imperative approach.
I could put just the relevant information into the functions and return the actions which will be taken for the given input. And one single function apply all the actions to the gamestate. But most functions need a lot of “relevant” information.
move() need the object position, the velocity, the map for collision, position of all enemys, current health, … So this approach does not seem to work either.
So my question is how do I handle the massive amount of state in a functional programming language — especially for game development?
EDIT: There are some game frameworks for building games in Clojure. There approach to solve this problem partially is to thread all objects in the game as “entities” and put it in a huge bag. A gigant main function is holding the screen and the entities and handle events (
n-init, …) for this entities and run the main display loop. But this is not the clean solution I am searching for.