ist xs = "The list is " ++ case xs of []  -> "empty."
                                               [x] -> "a singleton list."
                                               xs  -> "a longer list."


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