case_samples.hs

head' :: [a] -> a
head' [] = error "No Head"
head' (x:_) = x

head2' :: [a] -> a
head2' xs = case xs of [] -> error "No Head"
                       (x:_) -> x

describeList :: [a] -> String
describeList ls = "This list is" ++ case ls of [] -> " empty"
                                             [x] -> " a singleton list."
                                               xs -> " a longer list."

describeList2 :: [a] -> String
describeList2 ls = "The list is " ++ what ls
  where what [] = "empty"
        what [x] = "a singleton list."
        what xs = " a longer list."