Add few more drain implementations

fumieval · Nov 10, 2023 · 91b6b72 · 91b6b72
1 parent 81a1967
commit 91b6b72
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/witherable/src/Witherable.hs b/witherable/src/Witherable.hs
@@ -190,6 +190,7 @@ instance Witherable Maybe where
 
 instance Filterable Option where
  mapMaybe f = (>>= Option . f)
+ drain _ = Option Nothing
  {-# INLINE mapMaybe #-}
 
 instance Witherable Option where
@@ -207,6 +208,9 @@ instance Monoid e => Filterable (Either e) where
  mapMaybe f (Right a) = maybe (Left mempty) Right $ f a
  {-# INLINABLE mapMaybe #-}
 
+ drain (Left e) = Left e
+ drain (Right _) = Left mempty
+
 instance Monoid e => Witherable (Either e) where
  wither _ (Left e) = pure (Left e)
  wither f (Right a) = fmap (maybe (Left mempty) Right) (f a)