Haskell检查棋盘对角线运动是对还是错 [英] Haskell check if chess board diagonal movement is True or False

问题描述

我正在尝试编写4x5棋盘游戏，我想做一个简单的true false Bool函数，说明基于x，y坐标的移动是否为对角线.我想放置4个坐标2 x和2 y.我应该使用&&函数，例如我想放(1,1)和(2,2)吗?

I am trying to write a board game function of 4x5 board and I want to do a simple true false Bool function stating if the movement based on x,y coordinates is diagonal or not. I want to put 4 coordinates 2 x and 2 y. should I use the && function if for example I want to put (1,1) and (2,2)?

 isDiagonal x  
 if x == 1 && y == 1 then True
 else False
 isDiagonal x
 if x == 2 && y == 2 then True 
 else False

推荐答案

如果要检查点(x,y)是否与Haskell中的点(x',y')在同一对角线上，那么最好的起点是类型.

If you want to check if a point (x,y) is on the same diagonal as a point (x',y') in Haskell, a good place to start is with a type.

isDiagonal :: (Int, Int) -> (Int, Int) -> Bool

尽管在技术上是可选的，但最好的做法是为每个顶级函数都指定一个显式类型.

Whilst technically optional, it's good practice to give every top level function an explicit type.

现在，我们需要一个用于此功能的主体.

Now, we need a body for this function.

isDiagonal (x, y) (x', y') = ...

如果它们在相同的对角线上，则x和x'彼此之间的距离必须与y和y'一样远.这样我们就可以检查差异是否相等.即

If they're on the same diagonal, then x and x' must be as far apart from each other as y and y' are. So we can just check if the differences are equal. i.e

abs (x - x') == abs (y - y')

将它们放在一起，我们(希望)达到了所需的功能

Putting it all together, we (hopefully) arrive at the desired function

isDiagonal :: (Int, Int) -> (Int, Int) -> Bool
isDiagonal (x, y) (x', y') = abs (x - x') == abs (y - y')

这里完全不需要&&.但是我们可以使用它，例如，如果我们想施加一个额外的条件，例如新点必须位于4x5板上(假设使用1分索引)

There's no need for && here, at all. But we could use it, if for example we wanted to impose an extra condition, like the new points must be on the 4x5 board (assuming 1-indexing)

isDiagonal :: (Int, Int) -> (Int, Int) -> Bool
isDiagonal (x, y) (x', y') = x' >= 1 && x' <= 4 && 
                             y' >= 1 && y' <= 5 &&
                             abs (x - x') == abs (y - y')

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