Console interactivity in Netwire?

Question

I am testing with the Netwire haskell library and made it work with a simple time wire:

import Control.Wire
import Prelude hiding ((.), id)

import Control.Monad.IO.Class
import Data.Functor.Identity
import System.IO

wire :: (HasTime t s) => Wire s () m a t
wire = time

run :: (HasTime t s, MonadIO m, Show b, Show e) =>
       Session m s -> Wire s e m a b -> m ()
run session wire = do
  (dt, session') <- stepSession session
  (wt', wire') <- stepWire wire dt $ Right undefined
  case wt' of
    -- | Exit
    Left _ -> return ()
    Right x -> do
      liftIO $ do
        putChar '\r'
        putStr $ either (\ex -> show ex) show wt'
        hFlush stdout
        -- Interactivity here?
        gotInput <- hReady stdin
        if gotInput then
          return ()
          else return ()
      run session' wire'

main :: IO ()
-- main = testWire clockSession_ wire
main = run clockSession_ wire

Note: the run is basically modified from testWire, so I don't know if it is the correct way to form a network of wires. Part of the code origin from http://todayincode.tumblr.com/post/96914679355/almost-a-netwire-5-tutorial but that tutorial does not say about events.

Now I am trying to add a bit interactivity to the program. For now, quit the program when any key is pressed. I suppose I should do some event switching. However, I am stuck here because I cannot find a way to either change wire' or switch the behaviour. I tried to read the API document and the source, but I don't see how to actually "fire" an Event or using it to switch the wire.

Again, since I am not yet very familiar with Haskell, I may have made some big stupid mistakes here.

Update 1/2

I got my goal working by the following code. The timer stops on any key press. Update 2 I managed to separate out pollInput into another IO only function, Yay!

import Control.Wire
import Prelude hiding ((.), id)

import Control.Monad.IO.Class
import Data.Functor.Identity
import System.IO

wire :: (HasTime t s) => Wire s () m a t
wire = time

run :: (HasTime t s, MonadIO m, Show b, Show e) =>
       Session m s -> Wire s e m a b -> m ()
run session wire = do
  -- Get input here
  input <- liftIO $ pollInput

  (dt, session') <- stepSession session
  (wt', wire') <- stepWire wire dt $ input
  case wt' of
    -- | Exit
    Left _ -> liftIO (putStrLn "") >> return ()
    Right x -> do
      liftIO $ do
        putChar '\r'
        putStr $ either (\ex -> show ex) show wt'
        hFlush stdout

      run session' wire'

pollInput :: IO (Either a b)
pollInput =  do
  gotInput <- hReady stdin
  if gotInput then
    return (Left undefined)
    else return (Right undefined)


setup :: IO ()
setup = do
  hSetBuffering stdin NoBuffering
  hSetBuffering stdout NoBuffering


main :: IO ()
main = do
  setup
  run clockSession_ wire

However, this raises some further questions. First, is this good practise? Second, what is the type of pollInput? I tried to manually type it out but without success. Automatic type deduction works, though.

This is my explanation of how this code works:

First, the user input from console is polled, and after some logic, the "input" to wire is generated (poor name choice, but that input generated is the wire input) and passed along the network. Here, I simply pass an inhibition (Left something), and will cause the loop to exit. Of course, when exiting, the program produces a newline to make console look nicer.

(Well, I still don't understand how Event works, though)

Update 3/4

After reading @Cirdec 's answer, and fiddled a lot on my editor, I get this single threaded version without IORef, also quitting on pressing 'x'Update 4: (but it does not output anything):

import Control.Wire
import Prelude hiding ((.),id)
import Control.Wire.Unsafe.Event
import System.IO
import Control.Monad.IO.Class

data InputEvent = KeyPressed Char 
                | NoKeyPressed
                deriving (Ord, Eq, Read, Show)
type OutputEvent = IO ()

--- Wires
example :: (HasTime t s, Monad m, Show t) =>
           Wire s () m (Event [InputEvent]) (Event [OutputEvent])
example = switch $
          (fmap ((:[]) . print) <$> periodic 1 . time
           &&&
           fmap (const mkEmpty) <$> filterE (any (== KeyPressed 'x'))
           )

readKeyboard :: IO (Either e (InputEvent))
readKeyboard = do
  hSetBuffering stdin NoBuffering
  gotInput <- hReady stdin
  if gotInput then do
    c <- getChar
    return $ Right $ KeyPressed c
    else return $ Right $ NoKeyPressed

output :: [OutputEvent] -> IO ()
output (x:xs) = id x >> output xs
output _ = return ()

run :: (HasTime t s, MonadIO m) =>
       Session m s -> Wire s e m (Event [InputEvent]) (Event [OutputEvent]) -> m e
run = go
  where
    go session wire = do
      -- | inputEvent :: Event InputEvent
      inputEvent <- liftIO $ readKeyboard
      (dt, session') <- stepSession session
      (wt', wire') <- stepWire wire dt (Event <$> (fmap (:[]) inputEvent))
      -- (wt', wire') <- stepWire wire dt (Right undefined)
      case wt' of
        Left a -> return a
        Right bEvent -> do
          case bEvent of
            Event b -> liftIO $ output b
            _ -> return ()
          go session' wire'

main = do
  run clockSession_ example

I think this is much better than my original, but I am still not completely convinced whether it is good practise or not.

Answer 1

First, I would point to Kleisli Arrow in Netwire 5?. I came up with that answer after a longggg time of trying to understand Monads and Arrows. I will put a minimal example using Kleisli Wire soon.

This program merely echos what the user types, and quits when it hits a q. Though useless, it demonstrates a probably good practice of using Netwire 5.

mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a

This is the Kleisli wire constructor written in the answer in the post referenced. In summary, this function lifts any Kleisli function a -> m b into Wire s e m a b. This is the core about any I/O we are doing in this program.

Since we are echoing as user types, hGetChar is probably the best choice. Therefore, we lift that into a wire.

inputWire :: Wire s () IO () Char
inputWire = mkKleisli $ \_ -> hGetChar stdin

Similarly, we use the following wire to output characters on screen.

outputWire :: Wire s () IO Char ()
outputWire = mkKleisli $ putChar

Then to determine when we need to quit, a pure wire is constructed to output True when q is the input (Note that mkSF_ can be used instead of arr).

quitWire :: (Monad m, Monoid e) => Wire s e m Char Bool
quitWire = arr $ quitNow
    where 
      quitNow c 
          | c == 'q' || c == 'Q' = True
          | otherwise = False

To actually use the information of quitting, we need to write a special (but really simple) runWire function which runs a wire of type Wire s e m () Bool. When the wire is inhibited or returns false, the function ends.

runWire :: (Monad m) => Session m s -> Wire s e m () Bool -> m ()
runWire s w = do
  (ds, s') <- stepSession s
  (quitNow, w') <- stepWire w ds (Right ())
  case quitNow of
    Right False -> runWire s' w'
    _ -> return ()

Now, let's put wires together.

mainWire = inputWire >>> (quitWire &&& outputWire) >>> arr (\(q,_) -> q)

Of course we can use the Arrow syntax:

mainWire = proc _ -> do 
  c <- inputWire -< ()
  q <- quitWire -< c
  outputWire -< c
  returnA -< q

Not sure if the proc version is faster or not, but in this simple example, both are quite readable.

We get input from inputWire, feed it to both quitWire and outputWire and get a tuple (Bool, ()). Then we take the first one as the final output.

At last, we run everything in main!

main = do 
  hSetEcho stdin False 
  hSetBuffering stdin NoBuffering
  hSetBuffering stdout NoBuffering 
  runWire clockSession_ mainWire

Here comes the final code I used:

{-# LANGUAGE Arrows #-}

module Main where

import Control.Wire
import Control.Monad
import Control.Arrow
import System.IO
import Prelude hiding ((.), id)

mkKleisli :: (Monad m, Monoid e) => (a -> m b) -> Wire s e m a b
mkKleisli f = mkGen_ $ \a -> liftM Right $ f a

inputWire :: Wire s () IO () Char
inputWire = mkKleisli $ \_ -> hGetChar stdin

outputWire :: Wire s () IO Char ()
outputWire = mkKleisli $ putChar

quitWire :: (Monad m, Monoid e) => Wire s e m Char Bool
quitWire = arr $ quitNow
    where 
      quitNow c 
          | c == 'q' || c == 'Q' = True
          | otherwise = False

runWire :: (Monad m) => Session m s -> Wire s e m () Bool -> m ()
runWire s w = do
  (ds, s') <- stepSession s
  (quitNow, w') <- stepWire w ds (Right ())
  case quitNow of
    Right False -> runWire s' w'
    _ -> return ()

mainWire = inputWire >>> (quitWire &&& outputWire) >>> arr (\(q,_) -> q)

main = do 
  hSetEcho stdin False 
  hSetBuffering stdin NoBuffering
  hSetBuffering stdout NoBuffering 
  runWire clockSession_ mainWire