功能性香蕉旅行者 - 输入处理 [英] Functional Banana Traveller - Input Handling

问题描述

这是我的 Traveler 项目的一个子问题。

我已经将处理输入的粗糙代码放在一起。它的工作原理，直到我介绍 TChan 混合。以下是工作代码，并举例说明如何使用它。然后，我会改变它并解释我为什么这样做。然后，我会讨论这个问题。

  { - ＃LANGUAGE ScopedTypeVariables＃ - } 
 import Control.Monad （永久）
导入Control.Concurrent（forkIO）
导入Control.Monad.STM（STM，原子地）
导入Control.Concurrent.STM.TChan 
导入Reactive.Banana 
 import Reactive.Banana.Frameworks 
 
 
 data Planet = Vulcan 
 | Mars 
 | Terra 
导出（Eq，Read，Show）
 
数据命令=移动星球
 |看看
 |退出
 |无
派生显示
 
 makeNetworkDescription :: AddHandler（也许命令） - > IO EventNetwork 
 makeNetworkDescription addCommandEvent =编译$ do 
 eInput<  -  fromAddHandler addCommandEvent 
 let eCommand = filterJust eInput 
 bCommand = stepper Null eCommand 
 eCommandChanged<  -  changes bCommand 
 
 reactimate $（\\\
  - > appendFileoutput.txt（Command is++ show n））< $> 
 eCommandChanged 
  

执行 ghci



  ，Maybe Command  - > IO（））
 networkDescr<  -  makeNetworkDescription addCommandEvent 
 actuate networkDescr 
 return（Just $ Look）>> = fireCommand 
  

所以，现在我已经有了基本的机制，我想开始构建它。这将是一个多人游戏。解决这个问题的第一步就是从输入处理中获取来自 TChan 的输入。这个想法是，所有的玩家都会写这个 TChan ，每个命令都会按照它的顺序处理。

<所以我添加了一个新的函数'inputFrame'

  inputFrame :: TChan Command  - > IO（）
 inputFrame commandChannel = do 
（addCommandEvent，fireCommand）<  -  newAddHandler 
 networkDescr<  -  makeNetworkDescription addCommandEvent 
执行networkDescr 
 forkIO $ forever tryReadTChan commandChannel）>> = fireCommand 
 return（）
  

在 ghci 中使用它。

  commandChan<  -  atomically $ newTChan :: IO（TChan Command）
 _<  - 原子地$ writeTChan commandChan Look 
  

output.txt 不会被写入。正在读取 commandChan ，因为我在填充它后检查它是否为空。这显然是我做错了吗？如果没有，我该如何解决这个问题呢？此外，对于我的预期目的， TChan 是正确的选择吗？

解决方案

< （原子性）（tryReadTChan commandChannel）>> =您可能需要 fireCommand）

但我没有测试过这个。此外，在猜测，你可能会想在这里避免 tryReadTChan 。只需使用普通的 readTChan ，这样你就可以获得高效的重试而不是轮询。

This is a sub-problem from my Traveller project.

I've put together the rudementary code that will handle input. It works, until I introduce a TChan to the mix. Below is the working code, with an example of how to use it. Then, I will change it and explain why I am doing so. Then, I'll talk about the problem.

{-# LANGUAGE ScopedTypeVariables #-}
import Control.Monad (forever)
import Control.Concurrent (forkIO)
import Control.Monad.STM (STM,atomically)
import Control.Concurrent.STM.TChan
import Reactive.Banana
import Reactive.Banana.Frameworks


data Planet = Vulcan
            | Mars
            | Terra
                deriving (Eq,Read,Show)

data Command = Move Planet
             | Look
             | Quit
             | Null
                deriving Show

makeNetworkDescription :: AddHandler (Maybe Command) -> IO EventNetwork
makeNetworkDescription addCommandEvent = compile $ do
   eInput <- fromAddHandler addCommandEvent
   let eCommand = filterJust eInput 
       bCommand = stepper Null eCommand 
   eCommandChanged <- changes bCommand

reactimate $ (\n -> appendFile "output.txt" ("Command is " ++ show n)) <$>  
eCommandChanged

Executing the following in ghci will demonstrate that this works.

(addCommandEvent,fireCommand) <- newAddHandler :: IO (AddHandler (Maybe Command),Maybe Command -> IO ())
networkDescr <- makeNetworkDescription addCommandEvent
actuate networkDescr
return (Just $ Look) >>= fireCommand

So, now I have have the basic mechanism in place, I want to start building it out. This is going to be a multiplayer game. The first step in addressing this as far the the input handling goes is getting input from a TChan. The idea being, all players will write to this TChan, and each command will be processed in the order it arrived.

So I added a new function 'inputFrame'

inputFrame :: TChan Command -> IO ()
inputFrame commandChannel = do
   (addCommandEvent,fireCommand) <- newAddHandler
   networkDescr <- makeNetworkDescription addCommandEvent
   actuate networkDescr
   forkIO $ forever (atomically $ tryReadTChan commandChannel) >>= fireCommand
   return ()

Here is how I attempt to use it, in ghci.

commandChan <- atomically $ newTChan :: IO (TChan Command)
_ <- atomically $ writeTChan commandChan Look

output.txt doesn't get written to. commandChan is being read, as I check to see if it becomes empty after populating it. Is it obvious what I'm doing wrong? If not, how may I go about troubleshooting the problem? Also, for my intended purposes, is a TChan the right choice?

解决方案

You probably wanted

forkIO $ forever (atomically (tryReadTChan commandChannel) >>= fireCommand)

but I haven't tested this. Also, at a guess, you probably will want to avoid tryReadTChan here. Just use plain old readTChan, so that you get the efficient retry instead of polling.

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