How can a while loop be simulated in a functional language l

How can a while loop be simulated in a functional language like Haskell?

Solution

import Control.Monad while :: (a -> Bool) -> (a -> IO a) -> a -> IO a while praed funktion x | praed x = do y <- funktion x while praed funktion y | otherwise = return x power2 :: IO () power2 = do putStr \"Please enter a number.\" i <- getChar let praed x = x /= \' \' let f x = do putChar x getChar while praed f \'?\' return ()