an example from this page (http://www.haskell.org/haskellwiki/State_Monad) that I think is quite weak because it's easy to do by just folding over the string... But for the sake of comparison here we are!

State.hs

playGame :: String -> State GameState GameValue
playGame []     = do
    (_, score) <- get
    return score
 
playGame (x:xs) = do
    (on, score) <- get
    case x of
         'a' | on -> put (on, score + 1)
         'b' | on -> put (on, score - 1)
         'c'      -> put (not on, score)
         _        -> put (on, score)
    playGame xs

State1.elm

playGame : [Char] -> State GameState GameValue
playGame chars =
  case chars of
    [] -> with state
      let (_, score) <- get
      return score
 
    c::cs -> with state
      let (on, score) <- get
      case c of
        'a' -> if on then put (on, score + 1) else return ()
        'b' -> if on then put (on, score - 1) else return ()
        'c' -> put (not on, score)
        _   -> return ()

      playGame cs

State2.elm

-- introduces noOp and when to make "return ()" feel less weird

noOp : State s ()
noOp = return ()

when : Bool -> State s () -> State s ()
when b cmd = if b then cmd else return ()

playGame : [Char] -> State GameState GameValue
playGame chars =
  case chars of
    [] -> with state
      let (_, score) <- get
      return score
 
    c::cs -> with state
      let (on, score) <- get
      case c of
        'a' -> when on (put (on, score + 1))
        'b' -> when on (put (on, score - 1))
        'c' -> put (not on, score)
        _   -> noOp

      playGame cs