úÎV¥     NoneLike traverse:, but you can remove elements instead of updating them. #traverse f = wither (fmap Just . f) Minimal complete definition:  or .  is  with its arguments flipped.           witherable-0.1Data.Witherable Witherablewither catMaybeswitherMblightM$fWitherableSeq$fWitherableVector$fWitherableConst$fWitherableHashMap$fWitherableMap$fWitherableIntMap$fWitherable[]$fWitherableMaybe