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

Thank you, it was very helpfull. For reference, this is the code, that reflect Daniel's recommendation (I hope I made no stupid mistake there): https://github.com/satai/FrozenBeagle/blob/32f22979d7ef8d5265aa9e49982fa394e... Thanks Ondrej

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

...

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.

There's no problem defining values of type `RVar (Population -> Population`. `fmap allSurvive` is one such. But defining fairChance this way seems a bit awkward to me.

Daniel