2 files changed, 11 insertions, 7 deletions
diff --git a/users/grfn/xanthous/src/Xanthous/Data.hs b/users/grfn/xanthous/src/Xanthous/Data.hs
index c11ceb55aa26..1acd14a0640b 100644
--- a/users/grfn/xanthous/src/Xanthous/Data.hs
+++ b/users/grfn/xanthous/src/Xanthous/Data.hs
@@ -191,7 +191,7 @@ y = lens (\(Position _ yy) -> yy) (\(Position xx _) yy -> Position xx yy)
 
 type Position = Position' Int
 
-instance Arbitrary a => Arbitrary (Position' a) where
+instance (Arg (Position' a) a, Arbitrary a) => Arbitrary (Position' a) where
   arbitrary = genericArbitrary
   shrink (Position px py) = Position <$> shrink px <*> shrink py
 
@@ -313,7 +313,8 @@ data Direction where
   Here      :: Direction
   deriving stock (Show, Eq, Ord, Generic)
   deriving anyclass (CoArbitrary, Function, NFData, ToJSON, FromJSON, Hashable)
-  deriving Arbitrary via GenericArbitrary Direction
+
+deriving via (GenericArbitrary Direction) instance Arbitrary Direction
 
 instance Opposite Direction where
   opposite Up        = Down
@@ -432,7 +433,8 @@ data Neighbors a = Neighbors
   }
   deriving stock (Show, Eq, Ord, Functor, Foldable, Traversable, Generic)
   deriving anyclass (NFData, CoArbitrary, Function, MonoFoldable)
-  deriving Arbitrary via GenericArbitrary (Neighbors a)
+
+deriving via (GenericArbitrary (Neighbors a)) instance (Arg (Neighbors a) a, Arbitrary a) => Arbitrary (Neighbors a)
 
 type instance Element (Neighbors a) = a
 
@@ -768,9 +770,12 @@ data Box a = Box
   , _dimensions    :: V2 a
   }
   deriving stock (Show, Eq, Ord, Functor, Generic)
-  deriving Arbitrary via GenericArbitrary (Box a)
 makeFieldsNoPrefix ''Box
 
+-- It seems to be necessary to have an `Arg (V2 a) a` constraint, as a is passed
+-- to V2 internally, in order to make GHC figure out this deriving via correctly.
+deriving via (GenericArbitrary (Box a)) instance (Arg (V2 a) a, Arbitrary a) => Arbitrary (Box a)
+
 bottomRightCorner :: Num a => Box a -> V2 a
 bottomRightCorner box =
   V2 (box ^. topLeftCorner . L._x + box ^. dimensions . L._x)
diff --git a/users/grfn/xanthous/src/Xanthous/Orphans.hs b/users/grfn/xanthous/src/Xanthous/Orphans.hs
index 385873e7b464..b00c803cfe7a 100644
--- a/users/grfn/xanthous/src/Xanthous/Orphans.hs
+++ b/users/grfn/xanthous/src/Xanthous/Orphans.hs
@@ -22,6 +22,7 @@ import           Brick.Widgets.Core (getName)
 import           System.Random.Internal (StdGen (..))
 import           System.Random.SplitMix (SMGen ())
 import           Test.QuickCheck
+import           Test.QuickCheck.Arbitrary.Generic (Arg ())
 import           "quickcheck-instances" Test.QuickCheck.Instances ()
 import           Text.Megaparsec (errorBundlePretty)
 import           Text.Megaparsec.Pos
@@ -307,9 +308,7 @@ deriving stock instance Ord a => Ord (MaybeDefault a)
 deriving stock instance Ord Attr
 
 deriving anyclass instance Hashable Graphics.Vty.Input.Events.Key
-deriving anyclass instance NFData Graphics.Vty.Input.Events.Key
 deriving anyclass instance Hashable Graphics.Vty.Input.Events.Modifier
-deriving anyclass instance NFData Graphics.Vty.Input.Events.Modifier
 
 --------------------------------------------------------------------------------
 
@@ -374,7 +373,7 @@ deriving newtype instance (Arbitrary s, CoArbitrary (m (a, s)))
 
 --------------------------------------------------------------------------------
 
-deriving via (GenericArbitrary (V2 a)) instance Arbitrary a => Arbitrary (V2 a)
+deriving via (GenericArbitrary (V2 a)) instance (Arg (V2 a) a, Arbitrary a) => Arbitrary (V2 a)
 instance CoArbitrary a => CoArbitrary (V2 a)
 instance Function a => Function (V2 a)