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我想用haskell光泽创建一个简单的动画。我希望在前 4 秒，每个矩形都会将其颜色更改为较暗的颜色。问题是，经过较长时间的链接后，什么都没有发生——

在此处输入图像描述

所有矩形都出现并且它们不会改变颜色

这是我使用的以下代码 -

window :: Display
window = InWindow "Simon" (width, height) (offset, offset)

background :: Color
background = black

data SimonGame = Game {
    rectangleGreen::Picture, 
    rectangleRed::Picture,
    rectangleBlue::Picture,
    rectanglYellow::Picture
} deriving Show

initialState :: SimonGame
initialState = Game
  { rectangleGreen = translate (-100) (0) $ color green $ rectangleSolid 60 60,
    rectangleRed = translate (100) (0) $ color red $ rectangleSolid 60 60,
    rectangleBlue = translate (0) (100)  $  color blue $ rectangleSolid 60 60,
    rectanglYellow = translate (0) (-100)  $  color yellow $ rectangleSolid 60 60
  }

render :: SimonGame -> Picture 
render game = pictures
              [ rectangleGreen game,
                rectangleRed game,
                rectangleBlue game,
                rectanglYellow game
              ]

updateBoard :: Float-> SimonGame -> SimonGame 
updateBoard 1.0 game = game { 
                              rectangleGreen = translate (-100) (0) $ color (dark green)  $ rectangleSolid 60 60,
                              rectangleRed = translate (100) (0) $ color red $ rectangleSolid 60 60,
                              rectangleBlue = translate (0) (100)  $  color blue $ rectangleSolid 60 60,
                              rectanglYellow = translate (0) (-100)  $  color yellow $ rectangleSolid 60 60
                            }
updateBoard 2.0 game = game { 
                              rectangleGreen = translate (-100) (0) $ color green $ rectangleSolid 60 60,
                              rectangleRed = translate (100) (0) $ color (dark red) $ rectangleSolid 60 60,
                              rectangleBlue = translate (0) (100)  $  color blue $rectangleSolid 60 60,
                              rectanglYellow = translate (0) (-100)  $  color yellow $rectangleSolid 60 60
                            }                         
updateBoard 3.0 game = game {
                              rectangleGreen = translate (-100) (0) $ color green $ rectangleSolid 60 60,
                              rectangleRed = translate (100) (0) $ color red $ rectangleSolid 60 60,
                              rectangleBlue = translate (0) (100)  $  color (dark blue) $rectangleSolid 60 60,
                              rectanglYellow = translate (0) (-100)  $  color yellow $rectangleSolid 60 60
                            }
updateBoard 4.0 game = game { 
                              rectangleGreen = translate (-100) (0) $ color green $ rectangleSolid 60 60,
                              rectangleRed = translate (100) (0) $ color red $ rectangleSolid 60 60,
                              rectangleBlue = translate (0) (100)  $  color blue $rectangleSolid 60 60,
                              rectanglYellow = translate (0) (-100)  $  color (dark yellow) $rectangleSolid 60 60
                            }
updateBoard _ game = game

main :: IO ()
main = animate window background frame
  where
    frame :: Float -> Picture
    frame seconds = render $ updateBoard seconds initialState
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1 回答 1

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永远不要对浮点数进行相等检查。（或者，如果你这样做了，总是假设结果可能是False即使数字在概念上相等。）

在您的情况下，甚至在概念上都不是这种情况，因为animate在某些有限的时间点上被调用；为什么这些会包括任何确切的整数秒数？

解决此问题的一种简单方法是查找四舍五入到整秒的时间。

updateBoard :: Int -> SimonGame -> SimonGame 
updateBoard 1 game = game { ... }
updateBoard 2 game = game { ... }
...

main = animate window background frame
  where
    frame :: Float -> Picture
    frame seconds = render $ updateBoard (floor seconds) initialState
于 2017-10-28T14:34:32.050 回答