Implementation of null function

Question

I have to learn Haskell for university and therefor I\'m using learnyouahaskell.com for the beginning.
I always used imperative languages so I decided to practice Haskell

Answer 1

Because _ literally means anything apart from explicitly specified patterns. When you specify (_:_) it means anything which can be represented as a list containing at least 1 element, without bothering with what or even how many elements the list actually contains. Since the case with an explicit pattern for empty list is already present, (_:_) might as well be replaced by _.

However, representing it as (_:_) gives you the flexibility to not even explicitly pass the empty list pattern. In fact, this will work:

-- | Test whether a list is empty.
null                    :: [a] -> Bool    
null (_:_)              =  False
null _                  =  True

Demo