使用条件缩短Haskell中的字符串

shortenString :: String -> String
shortenString "hello" = "hi"
shortenString "goodbye" = "bye"
shortenString s = s

import Data.List

shortenString :: String -> String
shortenString s
  | "hello" `isPrefixOf` s = "hi" ++ drop (length "hello") s
  | "goodbye" `isPrefixOf` s = "bye" ++ drop (length "goodbye") s
  | otherwise = s

shortenString :: String -> String
shortenString [] = []
shortenString ('h':'e':'l':'l':'o':xs) = "hi" ++ shortenString xs
shortenString ('g':'o':'o':'d':'b':'y':'e':xs) = "bye" ++ shortenString xs
shortenString (x:xs) = x : shortenString xs