Question

你好，我试图用鳞片状的条件，但我得到解析错误：

parse error on input ‘|’ 

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

我在做什么错？谢谢

Answer 1

这是你想要的吗？

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

Guard条款按顺序检查。您最终只需要otherwise条款。

Answer 2

您还可以更地道与模式匹配这样写：

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