[Haskell-cafe] Re: Implementing Las Vegas algorithms in Haskell

Heinrich Apfelmus apfelmus at quantentunnel.de
Tue Jul 7 11:50:58 EDT 2009

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,


might help.



More information about the Haskell-Cafe mailing list