How do I implement the "game loop" in Erlang?

Question

I want to implement a game loop (that is acting as a server) in Erlang, but I dont know how to deal with the lack of incrementing variables.

What I want to do, described in Java code:

class Game {
    int posX, posY;
    int wall = 10;
    int roof = 20;

    public void newPos(x,y) {

        if(!collision(x,y)) {
            posX = x;
            posY = y;
        }
    }

    public boolean collision(x,y) {
        if(x == wall || y == roof) {
            // The player hit the wall.
            return true;         
        }
        return false;
    }

    public sendStateToClient() {
        // Send posX and posY back to client
    }


    public static void main(String[] args) {    

        // The game loop
        while(true) {

            // Send current state to the client
            sendStateToClient();

            // Some delay here...
        }
    }
}

If the client moves, then the newPos() function is called. This function changes some coordinate variables if a collision do not occur. The game loop is going on forever and is just sending the current state back to the client so that the client can paint it.

Now I want to implement this logic in Erlang but I dont know where to begin. I can't set the variables posX and posY in the same way as here... My only thaught is some kind of recursive loop where the coordinates is arguments, but I don't know if that is the right way to go either...

Answer 1

Your intuition is correct: a recursive loop with the state as a parameter is the standard Erlang approach.

This concept is often abstracted away by using one of the server behaviors in OTP.

Simple example, may contain errors:

game_loop(X, Y) ->
    receive
        {moveto, {NewX, NewY}} ->
            notifyClient(NewX, NewY),
            game_loop(NewX, NewY)
    end.