Heinrich, I saw you updated your operational package (you considered my
remark about ProgramView, thank you)
I saw you added a liftProgram function, however it is not like the mapMonad
function you were talking about.
mapMonad was:
mapMonad :: (Monad m1, Monad m2) =>
(forall a . m1 a -> m2 a)
-> ProgramT instr m1 a
-> ProgramT instr m2 a
and you turned it into the less generic:
liftProgram :: Monad m => Program instr a -> ProgramT instr m a
Did you change your mind?
2010/4/19 Heinrich Apfelmus
Limestraël wrote:
Okay, I start to understand better...
Just, Heinrich, how would implement the mapMonad function in terms of
Heinrich Apfelmus wrote: 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
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