如何解决有没有办法使用reactimate在Yampa中的getLine之外创建信号函数
我正在尝试编写一个简单的基于命令行的反射游戏,它将提示用户在随机时间后按 Enter 键,然后输出反应时间。我正在使用基于此示例的 reactimate:https://wiki.haskell.org/Yampa/reactimate 我的代码完全按照我的意愿运行:
module Main where
import Control.Monad
import Data.IORef
import Data.Time.Clock
import System.Random
import FRP.Yampa
main :: IO ()
main = do
startTime <- getCurrentTime
startTimeRef <- newIORef startTime
randomTime <- randomrIO (0,10)
reactimate helloMessage (sense startTimeRef) sayNow (randomTimePassed randomTime)
playerTime <- getCurrentTime
playerTimeRef <- newIORef playerTime
s <- getLine --programm will wait here
reactimate donothing (sense playerTimeRef) endMessage (enterpressed s)
Now <- getCurrentTime
let reactionTime = Now `diffUTCTime` playerTime in putStr (show reactionTime)
helloMessage :: IO ()
helloMessage = putStrLn "Press Enter as quickly as possible when I say so..."
randomTimePassed :: Double -> SF () Bool
randomTimePassed r = time >>> arr (>r)
sayNow :: Bool -> Bool -> IO Bool
sayNow _ x = when x (putStrLn "Now!") >> return x
donothing :: IO ()
donothing = return ()
enterpressed :: String -> SF () Bool --this is not how I want it to be
enterpressed s = arr (\_ -> s == "")
endMessage :: Bool -> Bool -> IO Bool
endMessage _ x = when x (putStr "You reacted in: ") >> return x
sense :: IORef UTCTime -> Bool -> IO (Double,Maybe ())
sense timeRef _ = do
Now <- getCurrentTime
lastTime <- readioRef timeRef
writeIORef timeRef Now
let dt = Now `diffUTCTime` lastTime
return (realToFrac dt,Just ())
但是对于我在代码中标记的按下输入部分,它根本没有使用 FRP。由于程序只是等待 getLine 终止,然后立即结束反应循环。所以它几乎只是使用 IO Monad 而不是 FRP。有什么方法可以重构信号函数 enterpressed
使其以“FRPish”方式工作?或者这在使用reactimate时根本不可能?
解决方法
这是一个似乎可以做您想做的事情的程序:
module Main where
import Control.Monad
import Data.IORef
import Data.Time.Clock
import FRP.Yampa
import FRP.Yampa.EventS
import System.IO
import System.Random
main :: IO ()
main = do
t <- getCurrentTime
timeRef <- newIORef t
randomTime <- randomRIO (0,10)
reactimate initialize (sense timeRef) actuate (signal randomTime)
signal :: Double -> SF (Event Char) (Event Out)
signal randomTime = after randomTime Prompt `andThen` waitForUser
waitForUser :: SF (Event Char) (Event Out)
waitForUser = arr id &&& time
>>> arr (\(e,t) -> mapFilterE (\c -> do guard (c == '\n'); pure (Enter t)) e)
data Out = Prompt | Enter Time
initialize :: IO (Event a)
initialize = do
putStrLn "Wait..."
pure NoEvent
actuate :: Bool -> Event Out -> IO Bool
actuate _ (Event Prompt) = putStrLn "Press now!" >> return False
actuate _ (Event (Enter t)) = True <$ putStrLn ("You responded in " ++ show t ++ " seconds")
actuate _ NoEvent = return False
sense :: IORef UTCTime -> Bool -> IO (Double,Maybe (Event Char))
sense timeRef _ = do
rdy <- hReady stdin
c <- if rdy
then Event <$> hGetChar stdin
else pure NoEvent
now <- getCurrentTime
lastTime <- readIORef timeRef
writeIORef timeRef now
let dt = now `diffUTCTime` lastTime
return (realToFrac dt,Just c)
为了稍微分解一下,我添加了一种感知键盘输入的方法:
sense timeRef _ = do
rdy <- hReady stdin
c <- if rdy
then Event <$> hGetChar stdin
else pure NoEvent
...
重要的是感知函数是非阻塞的,因为它也是决定反应程序“采样率”的东西。如果它会阻塞,例如使用 readLine
,那么计时器将永远不会达到提示显示所需的时间。
第二个重要变化是使用更丰富的输出事件类型:
data Out = Prompt | Enter Time
actuate :: Bool -> Event Out -> IO Bool
actuate _ (Event Prompt) = putStrLn "Press now!" >> return False
actuate _ (Event (Enter t)) = True <$ putStrLn ("You responded in " ++ show t ++ " seconds")
actuate _ NoEvent = return False
我确定的操作是在特定时间显示提示并按 Enter 键。这些足以实现所需的行为。
最后需要指定信号函数:
signal :: Double -> SF (Event Char) (Event Out)
signal randomTime = after randomTime Prompt `andThen` waitForUser
waitForUser :: SF (Event Char) (Event Out)
waitForUser = arr id &&& time
>>> arr (\(e,t) -> mapFilterE (\c -> do guard (c == '\n'); pure (Enter t)) e)
这分为两部分。第一部分等待程序开始时确定的随机时间。第二部分启动一个新的计时器(使用 time
信号函数)并等待换行符事件。如果发生这种情况,它会返回一个 enter 事件,其中包含用户按下 Enter 所需的时间。
语法有点复杂,如果我使用{-# LANGUAGE Arrows #-}
语法可能更容易阅读:
waitForUser :: SF (Event Char) (Event Out)
waitForUser = proc c -> do
t <- time -< ()
returnA -< case c of
Event '\n' -> Event (Enter t)
_ -> NoEvent
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