是否可以使用沒有案例的防護裝置重寫此 Haskell function？

Question

我有這個使用“case of”的 Haskell function，但我想弄清楚是否有可能重寫這個 function 使用警衛（“”）而不是“” 可能嗎？ 任何建議都會有所幫助。

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

您可以使用模式保護，因此：

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