解析输入错误'let'

-2

该代码需要一个四叉树并插入一个矩形。但是，我得到一个语法分析错误。我想调用函数newExtent而不必添加所有参数。所以newExtent TopLeft而不必拨打newExtent TopLeft extent rectangle。我如何使它工作？解析输入错误'let'

insert :: QuadTree -> Rectangle -> QuadTree 
insert (Qt extent horizontal vertical qTL qTR qBL qBR) rectangle  
    | quadPart extent rectangle == VerLine = Qt extent horizontal (rectangle:vertical) qTL qTR qBL qBR 
    | quadPart extent rectangle == HorLine = Qt extent (rectangle:horizontal) vertical qTL qTR qBL qBR 
    | quadPart extent rectangle == TopLeft && qTL == EmptyQuadTree = Qt extent horizontal vertical (newExtent TopLeft) qTR qBL qBR 
    | quadPart extent rectangle == TopLeft = Qt extent horizontal vertical (insert qTL rectangle) qTR qBL qBR 
    | quadPart extent rectangle == TopRight && qTR == EmptyQuadTree = Qt extent horizontal vertical qTL (newExtent TopRight) qBL qBR 
    | quadPart extent rectangle == TopRight = Qt extent horizontal vertical qTL (insert qTR rectangle) qBL qBR 
    | quadPart extent rectangle == BottomLeft && qBL == EmptyQuadTree = Qt extent horizontal vertical qTL qTR (newExtent BottomLeft) qBR 
    | quadPart extent rectangle == BottomLeft = Qt extent horizontal vertical qTL qTR (insert qBL rectangle) qBR 
    | quadPart extent rectangle == BottomRight && qBR == EmptyQuadTree = Qt extent horizontal vertical qTL qTR qBL (newExtent BottomRight) 
    | otherwise = Qt extent horizontal vertical qTL qTR qBL (insert qBR rectangle) 

    let (Rect eL eT eR eB) = extent 

    in newExtent :: TreeParts -> Rectangle -> Rectangle -> QuadTree 
     newExtent part (Rect eL eT eR eB) rectangle 
      | part == TopLeft = insert (emptyQtree (Rect eL eT ((eL + eR) `div` 2) ((eT + eB) `div` 2))) rectangle 
      | part == TopRight = insert (emptyQtree (Rect ((eL + eR) `div` 2) eT eR ((eT + eB) `div` 2))) rectangle 
      | part == BottomLeft = insert (emptyQtree (Rect eL ((eT + eB) `div` 2) ((eL + eR) `div` 2) eB)) rectangle 
      | part == BottomRight = insert (emptyQtree (Rect ((eL + eR) `div` 2) ((eT + eB) `div` 2) eR eB)) rectangle

来源

2015-02-07 quackAttack

更换您的让利块*请*阅读[哈斯克尔教程（http://stackoverflow.com/a/1016986/925978）。你不能在'let'语句中输入一个类型签名。 – crockeea 2015-02-07 14:20:20

谢谢，我修正了，但我仍然得到相同的错误... – quackAttack 2015-02-07 14:22:38

不要缩进插入

的类型签名in后，您不定义表达式功能。让语句允许您在in之后并且仅在那里定义可用于表达式的内容。在这种情况下，where声明可能会更容易。与这里的let语句相比，您可以在函数定义之后定义一些东西，并且可以在函数中使用它们，这看起来像是您正在尝试执行的操作。因此，试图通过

where (Rect eL eT eR eB) = extent 
     newExtent part 
      | part == TopLeft = insert (emptyQtree (Rect eL eT ((eL + eR) `div` 2) ((eT + eB) `div` 2))) rectangle 
      | part == TopRight = insert (emptyQtree (Rect ((eL + eR) `div` 2) eT eR ((eT + eB) `div` 2))) rectangle 
      | part == BottomLeft = insert (emptyQtree (Rect eL ((eT + eB) `div` 2) ((eL + eR) `div` 2) eB)) rectangle 
      | part == BottomRight = insert (emptyQtree (Rect ((eL + eR) `div` 2) ((eT + eB) `div` 2) eR eB)) rectangle

来源

2015-02-07 14:37:01 cocreature

谢谢！但它仍然不起作用。我仍然需要调用newExtent'newExtent TopLeft区域矩形'，是不是有办法解决它，所以'newExtent TopLeft'？ – quackAttack 2015-02-07 14:47:03

对不起，我不知何故错过了你的问题，更新了我的答案。 – cocreature 2015-02-07 14:51:50

而不是在where子句中对范围进行模式匹配，您可以直接在主函数定义中模式匹配。 – cocreature 2015-02-07 14:52:43

解析输入错误'let'

回答

相关问题