Folks,
I wonder if there is any particular reason for not having a class for object map of a functor (Functor-instances) in addition to the arrow map (fmap). Now you may say that this is just the constructor, but in my current example I have found it useful to have a general way of taking an object/value a into F a since the constructor can be arbitrary. I thought that I may need the return-operator in class Monad. I call it flift:
class Lift f where
flift :: a -> f aThis works nicely for trivial datatypes like "data Unit a = Unit" and "data Id a = Id a":
instance Lift Unit where
flift a = Unit instance Lift Id where
flift a = Id aMy question is --- how would you define Lift for constructors such as data Sum a = Inl a|Inr a and so forth?
Best Wishes, Johan Glimming
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