Daniel McAllansmith wrote:
Hello.
Given:
newtype Dist a = D {unD :: [(a,Int)]}
instance Monad Dist where return x = D [(x,1)] d >>= f = D [(y,q*p) | (x,p) <- unD d, (y,q) <- unD (f x)] fail _ = D []
How would one change Dist to wrap an instance of the (Data.Edison.Set c a) typeclass so that the Monad instance could be implemented in terms of e.g. singleton, unionWith, empty, etc?
I don't know about Data.Edison.Set, but if it's anything like base/Data.Set, then there's an Ord constraint on the elements, making it impossible to directly transform into a monad. However, Roberto Zunino came up with a clever way to bypass this problem with GADTS: http://article.gmane.org/gmane.comp.lang.haskell.cafe/18118 You may be able to apply this to your situation, using various Edison collections depending on which typeclasses your monad argument implements.