null package:containers

null :: IntMap a -> Bool
containers Data.IntMap.Internal Data.IntMap.Lazy Data.IntMap.Strict Data.IntMap.Strict.Internal
Is the map empty? 
Data.IntMap.null (empty)           == True
Data.IntMap.null (singleton 1 'a') == False
null :: IntSet -> Bool
containers Data.IntSet Data.IntSet.Internal
Is the set empty?
null :: Map k a -> Bool
containers Data.Map.Internal Data.Map.Lazy Data.Map.Strict Data.Map.Strict.Internal
Is the map empty? 
Data.Map.null (empty)           == True
Data.Map.null (singleton 1 'a') == False
null :: Seq a -> Bool
containers Data.Sequence Data.Sequence.Internal
Is this the empty sequence?
null :: Set a -> Bool
containers Data.Set Data.Set.Internal
Is this the empty set?