haskell - 创建一个矩形？ - haskell

Question

rectangleRaster :: Coord -> Coord -> Raster
rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])

矩形由两点定义:

data Shape
    = Point Point
    | Rectangle Point
                Point
    | Circle Point
            Point
    | Line Point
        Point
    | Polygon [Point]
    deriving (Show)

点定义为

type Point = (Double, Double)

地点:

type Shade = Double
type Coord = (Int, Int)

和

type Pixel = (Coord, Shade)
type Raster = [Pixel]

错误:

src\View.hs:70:24: error:
* Couldn't match type `Shape' with `[Pixel]'
  Expected type: Raster
    Actual type: Shape
* In the expression: (Rectangle [(a, 1)] [(b, 1)])
  In an equation for `rectangleRaster':
      rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |
70 | rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^

src\View.hs:70:34: error:
    * Couldn't match type `[(Coord, Integer)]' with `(Double, Double)'
      Expected type: Point
        Actual type: [(Coord, Integer)]
    * In the first argument of `Rectangle', namely `[(a, 1)]'
      In the expression: (Rectangle [(a, 1)] [(b, 1)])
      In an equation for `rectangleRaster':
          rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |
70 | rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |                                  ^^^^^^^^

src\View.hs:70:43: error:
    * Couldn't match type `[(Coord, Integer)]' with `(Double, Double)'
      Expected type: Point
        Actual type: [(Coord, Integer)]
    * In the second argument of `Rectangle', namely `[(b, 1)]'
      In the expression: (Rectangle [(a, 1)] [(b, 1)])
      In an equation for `rectangleRaster':
          rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |
70 | rectangleRaster a b = (Rectangle [(a, 1)] [(b, 1)])
   |            

不确定我做错了什么？这可能与 Raster 是 [Pixel] 列表有关，如果是这样，任何人都可以帮我解决这个问题吗？谢谢!

Answer 1

目前尚不清楚您想要做什么，但如果您想编写一个具有 rectangleRaster 给定类型的函数，则不必涉及 Rectangle。

看起来像OP的最简单的解决方案是这样的:

rectangleRaster :: Coord -> Coord -> Raster
rectangleRaster a b = [(a, 1), (b, 1)]

在这里，我将每个 Pixel 的 Shade 值硬编码为 1，因为这看起来像中尝试的解决方案OP。

您可以像这样调用该函数:

*Q50128894> rectangleRaster (1,2) (3,4)
[((1,2),1.0),((3,4),1.0)]

另一方面，如果您想要创建一个矩形，则需要提供两个Point 值，您可以像下面的 GHCi 中那样执行操作示例:

*Q50128894> Rectangle (1,2) (3,4)
Rectangle (1.0,2.0) (3.0,4.0)