> But for a game your state needs to update at specific time intervals, otherwise you walk too slow or too fast. How can that ever be purely expressed?
In this case you want ot have a system that reacts to an event that fires on a regular interval (as well as other sorts of input events). If you search for Functional Rdeactive Programming you will find some example libraries out there that try to do this in a pure manner (although I would personally have to say that this is all still a bit on the experimental side of things).
That said, Haskell still lets you do things the imperative way if you want! All you need to do is put the impure code in the IO monad, where it belongs.
You are only forced to be purely functional if you want to or if whoever is calling you must be a pure function. So basically, the idea is that your `main` function is impure code in the IO monad and it can call either more impure code or pure "helper" functions. Increasing the percentage of your code that is pure is a nice thing but its not mandatory.
In this case you want ot have a system that reacts to an event that fires on a regular interval (as well as other sorts of input events). If you search for Functional Rdeactive Programming you will find some example libraries out there that try to do this in a pure manner (although I would personally have to say that this is all still a bit on the experimental side of things).
That said, Haskell still lets you do things the imperative way if you want! All you need to do is put the impure code in the IO monad, where it belongs.
You are only forced to be purely functional if you want to or if whoever is calling you must be a pure function. So basically, the idea is that your `main` function is impure code in the IO monad and it can call either more impure code or pure "helper" functions. Increasing the percentage of your code that is pure is a nice thing but its not mandatory.