This module provides a comonadic interface to random values. In some situations, this may be more natural than a monadic approach.

The following function generates an infinite list of dice throw sums with n dice.

 rolls :: RandomGen g => Int -> g -> [Int]
 rolls n =
     extracts left          .  -- Extract an infinite list of the sums.
     fmap (sum . take n)    .  -- Sum the first n values of each list.
     extend (extracts next) .  -- Group them into lists of die values.
     mkRandR (1,6)             -- Generate random die values.

One potential gotcha with this library is that a top-level Rand that is extracted deeply could result in a space leak due to the memoization. It's a good idea to try not to hold on to Rands for longer than necessary.