On 30/07/15 20:38, Zemyla wrote:
Normally, a monad transformer to provide a random number generator would be of the form StateT g, where g is a RandomGen. But I've seen some libraries (like QuickCheck) define their RandomT as:
newtype RandomT g m a = RandomT { runRandomT :: g -> m a }
with their monadic bind operation defined as
(RandomT m) >>= f = RandomT $ \g -> let (ga, gb) = split g in m ga >>= (\a -> runRandomT (f a) gb)
and return and fail as in ReaderT.
Can someone describe the advantages and disadvantages of doing RandomT this way? I mean, if your generator has a subpar split operation (and most do), this will obviously exacerbate any problems with it.
tf-random addresses this.
Does it give any comparable advantages?
It doesn't introduce data dependencies. Let's say you generate a random binary tree. With the split approach, you can take the right subtree without evaluating the left one. Roman