无法将预期类型“IO ()”与实际类型“(Controller -> IO ()) -> IO ()”匹配

Question

我是 Haskell 的新手，我在尝试配置代码时遇到了这个错误。我知道 main() 中的所有指令都必须是 IO()，并且发生错误是因为我使用的函数之一（在 Graphics.Gloss.Interface.IO.Animate 中）没​​有返回 IO()。我想通过使用光泽包显示遗传算法的结果。 这是我的代码：

module Main where

import Prelude as P
import Control.Monad.Random as Rand
import Data.Functor
import Data.IORef
import Graphics.Gloss.Interface.IO.Animate
import Graphics.Solution
import Graphics.Plot

import Args
import Task
import Parsing
import Genetic

import Control.Concurrent.Async
import Control.Concurrent.STM.TChan
import Control.Monad.STM
import Control.Arrow (first)


main :: IO ()
main = do
  args <- parseOptions 

  opts <- loadEvolOptions (evolOptionsFileName args)
  gen <- newStdGen
  task@(Task _ twrs _ _) <- loadTask (inputFileName args) (fitnessFuncFileName args)

  chan <- newTChanIO
  asolution <- async $ solve chan gen opts task
  dataRef <- newIORef []
  finalSolutionRef <- newIORef Nothing

  animateIO mode white $ const $ do
      mfinsol <- readIORef finalSolutionRef
      case mfinsol of
        Just solution -> do
          samples <- readIORef dataRef
          return $ solutionPicture task solution (fitnessPlot samples)
        Nothing -> do
          msolution <- poll asolution     
          case msolution of
            Nothing -> do
              mv <- atomically $ tryReadTChan chan
              case mv of
                Nothing -> return ()
                Just v -> modifyIORef dataRef (++[v])
              samples <- readIORef dataRef
              return $ fitnessPlot samples
            Just esol -> case esol of
              Left e -> fail $ show e
              Right solution -> do
                saveResult (outputFileName args) (filterTowers solution twrs)
                writeIORef finalSolutionRef (Just solution)
                samples <- readIORef dataRef
                return $ solutionPicture task solution (fitnessPlot samples)
      where mode = InWindow "test_genetic_al" (1280, 1024) (10, 10)
            fitnessPlot ds =  translate (-300) (-200) $ scale 600 600 $ plot "generation" "fitness" $ first fromIntegral <$> ds

这是我得到的：

Couldn't match expected type ‘IO ()’
                with actual type ‘(Controller -> IO ()) -> IO ()’
    In a stmt of a 'do' block:
      animateIO mode white
      $ const
        $ do { mfinsol <- readIORef finalSolutionRef;
               case mfinsol of {
                 Just solution -> do { ... }
                 Nothing -> do { ... } } }
    In the expression:
      do { args <- parseOptions;
           opts <- loadEvolOptions (evolOptionsFileName args);
           gen <- newStdGen;
           task@(Task _ twrs _ _) <- loadTask
                                       (inputFileName args) (fitnessFuncFileName args);
           .... }
    In an equation for ‘main’:
        main
          = do { args <- parseOptions;
                 opts <- loadEvolOptions (evolOptionsFileName args);
                 gen <- newStdGen;
                 .... }
          where
              mode = InWindow "test_genetic_al" (1280, 1024) (10, 10)
              fitnessPlot ds
                = translate (- 300) (- 200)
                  $ scale 600 600
                    $ plot "generation" "fitness" $ first fromIntegral <$> ds

我已经在 Google 和 stackoverflow 上搜索了很多次我的问题，但仍然找不到解决此错误的方法。请帮帮我。

P/S：这是 Graphics.Gloss 的指南：https://hackage.haskell.org/package/gloss-1.11.1.1/docs/Graphics-Gloss-Interface-IO-Animate.html

再次抱歉我的愚蠢问题，在我给出 Lazersmoke 的建议（你可以在下面的评论区看到）之后，我得到了另一个与我要求的错误非常相似的错误：

我改行：animateIO mode white $ const $ do

进入：animateIO模式白(_->return())$const$do

Couldn't match type ‘Picture’ with ‘()’
    Expected type: Controller -> IO ()
      Actual type: Controller -> IO Picture
    In the second argument of ‘($)’, namely
      ‘const
       $ do { mfinsol <- readIORef finalSolutionRef;
              case mfinsol of {
                Just solution -> do { ... }
                Nothing -> do { ... } } }’
    In a stmt of a 'do' block:
      animateIO mode white (\ _ -> return ())
      $ const
        $ do { mfinsol <- readIORef finalSolutionRef;
               case mfinsol of {
                 Just solution -> do { ... }
                 Nothing -> do { ... } } }
    In the expression:
      do { args <- parseOptions;
           opts <- loadEvolOptions (evolOptionsFileName args);
           gen <- newStdGen;
           task@(Task _ twrs _ _) <- loadTask
                                       (inputFileName args) (fitnessFuncFileName args);
           .... }

Answer 1

animateIO 接受多少个参数？

animateIO :: Display    
          -> Color  
          -> (Float -> IO Picture)  
          -> (Controller -> IO ())  
          -> IO ()

四个。您向animateIO 提供了多少个参数？

animateIO mode white $ …

三个。类型

animateIO mode white $ …

是(Controller -> IO ()) -> IO ()，这正是您的错误消息告诉您的内容。由于您不想使用Controller -> IO () 部分，您可以提供自己的animateIO：

animateIO' :: Display -> Color -> IO Picture -> IO ()
animateIO' m c a = animateIO m c (const a) (const $ return ())

请注意，您的 (\_ -> return ()) 不起作用，因为第三个参数必须生成 Picture，而不是 IO ()。