Add Foldable instance for Day #7
Conversation
| @@ -117,3 +124,9 @@ instance comonadDay :: (Comonad f, Comonad g) => Comonad (Day f g) where | |||
|
|
|||
| instance comonadTrans :: Comonad f => ComonadTrans (Day f) where | |||
| lower = runDay \get fx gy -> get (extract fx) <$> gy | |||
|
|
|||
| instance foldableDay :: (Foldable f, Foldable g) => Foldable (Day f g) where | |||
There was a problem hiding this comment.
This seems like an unusual choice of instance to me. That length (day _ fx gy) is length fx * length gy seems a bit strange. I know Foldable has no laws to satisfy, but still. I noticed this instance also isn't present in kan-extensions, so I'd be interested to hear if there's a reason why.
There was a problem hiding this comment.
My only real motivation for this was that it felt like it should have one, similar to how the Coyoneda instance works:
toList (coyoneda t f) ≅ t <$> toList f
toList (day t f g) ≅ t <$> toList f <*> toList gI'd also be interested to hear both: why it's not present in kan-extensions; and which alternative instances are possible.
| @@ -94,6 +96,11 @@ assoclDay = runDay \phi f x -> runDay (\psi g h -> day identity (day (\a b c -> | |||
| assocrDay :: forall f g h. (f ⊗ g) ⊗ h ~> f ⊗ (g ⊗ h) | |||
| assocrDay = runDay \phi x h -> runDay (\psi f g -> day (#) f (day (\a b c -> phi (psi c a) b) g h)) x | |||
|
|
|||
| tupleDay :: forall f g x y . f x -> g y -> Day f g (Tuple x y) | |||
There was a problem hiding this comment.
I feel like this maybe crosses the Fairbairn threshold. I'm curious what you use it for?
There was a problem hiding this comment.
This was mainly to facilitate the above example. Will happily delete!
|
Thanks for your feedback @paf31 ✨ |
Also added
tupleDay(<⊗>), for example:Wasn't sure what to call the function and it's operator, feel free to rename.