Re: [Haskell-beginners] Random variable holding a function

Daniel Bergey wrote:

On 2015-02-26 at 12:42, Ondrej Nekola wrote:

...

I try to simulate some processes, that contain randomness and I would like do it idiomatic way and keep as much code not to know about randomness as possible.

type Selection = Population -> Population

so far, it's easy:

allSurvive :: Selection allSurvive = id

fairChance :: Int -> Population -> RVar Population fairChance newSize p = Population <$> (Data.Random.Extras.sample newSize $ individuals p)

fairChance :: Int -> RVar Selection (e.g. fairChance :: Int -> RVar (Population -> Population))

Is there a way to do this? Or should I give up this way and try to give up some purity and go withtype Selection :: RVar Population -> RVar population?

I would define Selection as

| type Selection = Population -> RVar Population

Then you can compose with >>=, which specializes to

| (>>=) :: RVar Population -> Selection -> RVar Population

or with any of the other Monad operators (eg, >=>).

With this definition, you can keep your current definition of fairChance.

This is pretty much the "probability monad". For more on this, my personal recommendations would be http://apfelmus.nfshost.com/articles/random-permutations.html http://web.engr.oregonstate.edu/~erwig/papers/PFP_JFP06.pdf Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com