State Monad, sequences of random numbers and monadic code

Question

I\'m trying to grasp the State Monad and with this purpose I wanted to write a monadic code that would generate a sequence of random numbers using a Linear Congruential Gene

Answer 1

You've got a couple great responses. What I do when working with the State monad is in my mind replace State s a with s -> (s,a) (after all, that's really what it is).

You then get a type for bind that looks like:

(>>=) :: (s -> (s,a)) ->
         (a -> s -> (s,b)) ->
         (s -> (s,b))

and you see that bind is just a specialized kind of function composition operator, like (.)

I wrote a blog/tutorial on the state monad here. It's probably not particularly good, but helped me grok things a little better by writing it.