Heinrich Apfelmus wrote:
Limestraël wrote:
Okay, I start to understand better...
Just, Heinrich, how would implement the mapMonad function in terms of the operational package? You just shown the signature.
Ah, that has to be implemented by the library, the user cannot implement this. Internally, the code would be as Bertram suggests:
mapMonad :: (Monad m1, Monad m2) => (forall a . m1 a -> m2 a) -> ProgramT instr m1 a -> ProgramT instr m2 a mapMonad f (Lift m1) = Lift (f m1) mapMonad f (Bind m k) = Bind (mapMonad f m) (mapMonad f . k) mapMonad f (Instr i) = Instr i
Silly me! This can be implement by the user: mapMonad f = id' <=< lift . f . viewT where id' :: ProgramViewT instr m1 a -> ProgramT instr m2 a id' (Return a) = return a id' (i :>>= k) = singleton i >>= mapMonad f . k and it would be a shame for the operational approach if that were not possible. :) Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com