Read until end of stream in haskell

Question

I\'m fairly new to Haskell, and I\'d like to keep reading lines from the console until the end of the stream, and outputting everything I get in upper case. So far, I\'ve got

Answer 1

This goes way beyond what you're really asking for, but I use this pattern a lot: interact:

myFun :: String -> String
myFun = ...

main = interact (unlines . myFun . lines)

Your function myFun will be executed against every line of standard input and the result sent to standard output.

Answer 2

You could also just rely on lazy IO.

import Data.Char

main :: IO ()
main = do
   inp <- getContents
   let ls = lines inp
       upcased = map (map toUpper) ls
   mapM_ putStrLn upcased

Answer 3

Another option is to use when whose documentation can be found here:

import System.IO (isEOF)
import Data.Char (toUpper)
import Control.Monad (forever, when)
import System.Exit (exitSuccess)
main = myLoop

myLoop = forever $ do
                done <- isEOF
                when done $ putStrLn "Bye!" >> exitSuccess
                inp <- getLine
                putStrLn (map toUpper inp)
                myLoop

Otherwise, the answer is identical to the one by @dave4420.

Answer 4

Use isEOF from System.IO.

import System.IO (isEOF)
import Data.Char

main = myLoop

myLoop = do done <- isEOF
            if done
              then putStrLn "Bye!"
              else do inp <- getLine
                      putStrLn (map toUpper inp)
                      myLoop