Simple commandline/eval loop in Haskell

Played with Haskell a little more, and put together a simple eval loop that you can tie your own functions to. It gives a prompt, reads input, calls a function on that input, and then loops again. The next step is probably to put an honest parser on it, but for now I think it shows off how simply you can do the loop. (There may be even better ways, if you know of one post a comment)

doSomething s = 
  "**" ++ s ++ "**"

commandln = do 
  putStr "> "  
  x <- getLine
  if x == "quit" 
    then return () 
    else putStrLn (doSomething x) >> commandln

Edit: Does anyone know if that's tail-recursive? And, if it's not, how it could be changed to be?