Luke Palmer wrote:
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.
Yes, but I only need the random values inside splitOnMedia. The rest is just non-linear plumbing. We do not know beforehand how many random values a branch quicksort will consume --- neither do we ware about the state of the random generator at the end. Do you consider the RandomMonad the best fit?
Random monad is a very natural choice for "random cloud" computations. Don't think of it as a state monad -- that's an implementation detail. You can think of a value of type Random a as a "probability distribution of a's"; and there are natural definitions for the monad operators on this semantics.
I blogged about this a while ago: http://lukepalmer.wordpress.com/2009/01/17/use-monadrandom/
I concur with Luke that interpreting Random a as a probability distribution of values of type a is the best mental model. The fact that it's a monad is secondary, if crucial for doing anything with these values. For a concrete example, http://apfelmus.nfshost.com/random-permutations.html might help. Regards, apfelmus -- http://apfelmus.nfshost.com