Question

你好，我試圖用鱗片狀的條件，但我得到解析錯誤：

parse error on input ‘|’ 

isAssignMent::String->Bool 
isAssignMent a 
    | a == "" = False 
    | otherwise 
     | (head trimmed) == '=' = True 
     | otherwise = False 
     where 
      trimmed = trimRightSide a [' ', '\n'] 

我在做什麼錯？謝謝

Answer 1

這是你想要的嗎？

isAssignMent::String->Bool 
isAssignMent a 
    | a == "" = False 
    | (head trimmed) == '=' = True 
    | otherwise = False 
     where 
      trimmed = trimRightSide a [' ', '\n'] 

Guard條款按順序檢查。您最終只需要otherwise條款。

Answer 2

您還可以更地道與模式匹配這樣寫：

isAssignMent::String->Bool 
isAssignMent ""   = False 
isAssignMent a 
    | '=':_ <- trimmed = True 
    | otherwise   = False 
    where 
     trimmed = trimRightSide a [' ', '\n']