Matthias Görgens
Yes, I thought of a similar scheme. Say we want to implemented randomized quicksort. Passing a list of random numbers would destroy laziness and linearise the algorithm --- because the right recursion branch would need to know at least how many random numbers where consumed by the left branch.
Well, you could implement a function 'split' as split (x:xs) = (evens (x:xs), evens xs) where evens (y:_:ys) = y:evens ys This would divide your supply of random numbers in two - this is lazy, but forcing any of the sublists would force the spine of the original list, so not optimal. So the obvious followup is why not pass a randomGen around instead, which has a split operation already defined, and which causes no laziness headaches?
What I wondered was, if one could hid the random plumbing in some data structure, like the state monad, but less linear.
This problem cries for a State monad solution - but you don't need to do it yourself, there's already a Random monad defined for you. -k -- If I haven't seen further, it is by standing in the footprints of giants