是否可以使用没有案例的防护装置重写此 Haskell function？

Question

I have this Haskell function that uses "case of", but I am trying to figure out if it's possible to rewrite this function using guards("|") and not "case of". Is it possible? Any suggestion would be helpful.

lefQ :: Ord a => LOL a -> Lang a -> Lang a
lefQ (LOL i xs) [] = []
lefQ (LOL i xs) (LOL j y:ys) = case stripPrefix xs y of
                    Nothing -> leftq (LOL i xs) ys
                    Just zs -> (LOL (j-i) zs):lefQ (LOL i xs) ys

Answer 1

You can work with a pattern guard , so:

lefQ :: Ord a => LOL a -> Lang a -> Lang a
lefQ (LOL i xs) [] = []
lefQ (LOL i xs) (LOL j y:ys)
    | Just zs <- stripPrefix xs y = (LOL (j-i) zs): lefQ (LOL i xs) ys
    | otherwise = leftq (LOL i xs) ys