如何修复缩进？Haskell:输入`'；

所以我得到了一个错误：

error:
parse error on input `|'

   | x == 'a' = True

守则本身是：

module SubstitutionCiphers where
import AssignmentHelp.Cipher

validateCipher ::  Cipher -> Boolean
  validateCipher "" = False
  validateCipher (x:xs) 
    | x == 'a' = True
    | otherwise = validateCipher xs

---

我试着以各种不同的方式交替压痕，但似乎没有任何效果。我想这仍然是一个缩进问题，但我不知道如何解决它。

您不应该缩进签名下面的部分。只需这样写：

validateCipher ::  Cipher -> Bool
validateCipher "" = False
validateCipher (x:xs)
    | x == 'a' = True
    | otherwise = validateCipher xs

或者，您可以通过以下方式进行检查：

validateCipher :: Cipher -> Bool
validateCipher = elem 'a'

---

当您缩进定义的第一行时，解析器（在此上下文中）认为您在继续上一行，就好像您编写了

validateCipher :: Cipher -> Bool validateCipher "" = False -- etc

这一点通过一个更简单的定义变得显而易见

validateCipher :: String -> Bool
  validateCipher _ = True

因为解析器能够接受这一点。但是，类型签名的结果位置无效

<interactive>:11:1: error:
    Illegal type signature: ‘String -> Bool validateCipher _’
      Type signatures are only allowed in patterns with ScopedTypeVariables

请不要在签名下缩进零件。

validateCipher ::  Cipher -> Bool
validateCipher "" = False
validateCipher (x:xs) 
  | x == 'a' = True
  | otherwise = validateCipher xs