Haskell 在何处分析错误

在此代码中

neighbours :: CityMap -> District -> [District]
neighbours (CM (_,rs)) b = mapMaybe neighbour rs
    where neighbour (p,q)
        | b == p    = Just q --parse error (possibly incorrect indentation or mismatched brackets)
        | b == q    = Just p
        | otherwise = Nothing

---

我必须首先解析«|»

防护装置的缩进必须比它们所属函数的名称更深，例如：

neighbours :: CityMap -> District -> [District]
neighbours (CM (_,rs)) b = mapMaybe neighbour rs
    where neighbour (p,q)
           | b == p    = Just q 
           | b == q    = Just p
           | otherwise = Nothing

这是因为在where之后，您定义了一个（本地）函数

neighbor

，它也必须遵循布局规则；如果防护装置更靠左，则它不是

邻居定义的延续。您会在一个类似以下内容的文件中遇到相同的错误：

  neighbour (p,q)
| b == p   = Just q

防护装置的缩进深度必须超过其所属功能的名称，例如：

neighbours :: CityMap -> District -> [District]
neighbours (CM (_,rs)) b = mapMaybe neighbour rs
    where neighbour (p,q)
           | b == p    = Just q 
           | b == q    = Just p
           | otherwise = Nothing

这是因为在where之后，您定义了一个（本地）函数
neighbor
，它也必须遵循布局规则；如果防护装置更靠左，则它不是
邻居定义的延续。您会在一个类似以下内容的文件中遇到相同的错误：

  neighbour (p,q)
| b == p   = Just q

检查缩进。制表符是8个空格。@chirlu，我用了4个空格。我想你的守卫需要超过缩进的开头。制表符是8个空格。@chirlu，我用4个空格。我想你的卫兵需要超过邻居的开头