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

import Data.Char

main = myLoop

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

However, I can’t seem to figure out how to avoid the if (inp == "x") condition and replace it with an end of stream condition.

In short, I’m looking for Haskell’s equivalent to while (cin >> line) in C++

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.