Haskell Language 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