Haskell顯示解析錯誤

Question

有人可以幫我嗎？我試圖運行average功能，但我得到的是讀取錯誤「（語法錯誤）上輸入‘::’」此代碼：

sum` :: [Int] -> Int 
sum` [] = 0 
sum` (x:xs) = x + sum` xs 

length` :: [a] -> Int 
length` [] = 0 
length` (x:xs) = 1 + length` xs 

average :: [Int] -> Rational 
average [] = error "empty list" 
average xs = toRational (sum xs)/toRational(length xs) 

非常感謝

Answer 1

按的意見評論，我提出我的一個答案評論：

我不認爲你可以使用反引號（`），請嘗試使用單引號（'）

所以它會是：

sum' :: [Int] -> Int 
sum' [] = 0 
sum' (x:xs) = x + sum' xs 

length' :: [a] -> Int 
length' [] = 0 
length' (x:xs) = 1 + length' xs 

average :: [Int] -> Rational 
average [] = error "empty list" 
average xs = toRational (sum xs)/toRational(length xs