feat(xan): Use Witherable in the prelude r/1110

Install the witherable library, expose it in the prelude, and update all
call sites that are broken by that change.

This is a really nice library, and basically the ideal abstraction layer
for what it does.

Change-Id: I640e099318c1ecce0ad483bc336c379698bdab88
Reviewed-on: https://cl.tvl.fyi/c/depot/+/725
Reviewed-by: glittershark <grfn@gws.fyi>

1 files changed, 4 insertions, 1 deletions

diff --git a/users/glittershark/xanthous/src/Xanthous/Data.hs b/users/glittershark/xanthous/src/Xanthous/Data.hs
index 3cb74bdca9..67173cc896 100644
--- a/users/glittershark/xanthous/src/Xanthous/Data.hs
+++ b/users/glittershark/xanthous/src/Xanthous/Data.hs
@@ -387,8 +387,11 @@ data Neighbors a = Neighbors
   , _bottomRight :: a
   }
   deriving stock (Show, Eq, Ord, Functor, Foldable, Traversable, Generic)
-  deriving anyclass (NFData, CoArbitrary, Function)
+  deriving anyclass (NFData, CoArbitrary, Function, MonoFoldable)
   deriving Arbitrary via GenericArbitrary (Neighbors a)
+
+type instance Element (Neighbors a) = a
+
 makeFieldsNoPrefix ''Neighbors
 
 instance Applicative Neighbors where