NodeJS.hs

import Control.Monad.Reader
import System.IO
import System.Process

data NodeJS = NodeJS
    { nodeIn :: Handle
    , nodeOut :: Handle
    , nodeErr :: Handle
    , nodePid :: ProcessHandle
    }

type NodeT = ReaderT NodeJS

runNodeJS :: MonadIO m => String -> NodeT m a -> m a
runNodeJS command action = do
    (inp, out, err, pid) <- liftIO $ runInteractiveCommand command
    forM_ [inp, out, err] $ \h -> liftIO $ hSetBinaryMode h False
    runReaderT action $ NodeJS inp out err pid

node :: MonadIO m => String -> NodeT m String
node expr = do
    n <- ask
    liftIO $ hPutStrLn (nodeIn n) $ "console.log(" ++ expr ++ ");"
    liftIO $ hGetLine (nodeOut n)

good :: IO String
good = runNodeJS "node" $ node "1+1"

good' :: IO Bool
good' = runNodeJS "node" $ fmap (== "2") (node "1+1")

bad :: IO Bool
bad = runNodeJS "node" $ do
    x <- node "1+1"
    return $ x == "2"