Haskell Language Foldable Checking if a Foldable structure is empty
Example
null returns True if there are no elements a in a foldable structure t a, and False if there is one or more. Structures for which null is True have a length of 0.
ghci> null []
True
ghci> null [14, 29]
False
ghci> null Nothing
True
ghci> null (Right 'a')
False
ghci> null ('x', 3)
False
null is defined as being equivalent to:
class Foldable t where
-- ...
null :: t a -> Bool
null = foldr (\_ _ -> False) True
