Applicative Output

[AshleyYakeley]

It should be possible to create instances roughly along these lines:

instance {-# OVERLAPPABLE #-} (Applicative f, Rangeable a) => Rangeable (f a)
instance {-# OVERLAPPABLE #-} (Applicative f, IsInline a) => IsInline (f a)
instance {-# OVERLAPPABLE #-} (Applicative f, HasAttributes a) => HasAttributes (f a)
instance {-# OVERLAPPABLE #-} (Applicative f, IsBlock il b) => IsBlock (f il) (f b)
-- etc.

Alternatively, if overlapping instances are scary, one could create a wrapper type:

newtype Wrapper (f :: Type -> Type) (a :: Type) = Wrapper (f a) deriving (Functor, Applicative)
instance (Applicative f, Rangeable a) => Rangeable (Wrapper f a)
instance (Applicative f, IsInline a) => IsInline (Wrapper f a)
instance (Applicative f, HasAttributes a) => HasAttributes (Wrapper f a)
instance (Applicative f, IsBlock il b) => IsBlock (Wrapper f il) (Wrapper f b)
-- etc.

Is this something you'd consider?

[jgm]

Can you say a bit more about what you are trying to do and why you want this?

[AshleyYakeley]

So, I can actually do this in a separate module. I don't need to modify commonmark to do this. So this is not at all urgent for me.

It's just that I have a type WholeModel that is Applicative, but not Monad. I want to convert text in CommonMark format to WholeModel (Html ()), using a custom SyntaxSpec that interprets a particular syntax.

Now I could just define instance IsBlock il b => IsBlock (WholeModel il) (WholeModel b), etc., but those instances can actually be generalised to any applicative type: instance (Applicative f, IsBlock il b) => IsBlock (f il) (f b).

[AshleyYakeley]

I created a PR (#163).

[AshleyYakeley]

#163 fixed this