A brutalized Haskell programmer

In working on a special Xmas lecture for my 1st semester course, I was going through Fritz Ruehr's "The Evolution of a Haskell Programmer" only to notice that there is no imperatively faked version that uses references. This omission could be resolved with the following code:

module Control.Pascal where

import Data.IORef

while :: IORef a -> (a -> Bool) -> IO () -> IO ()
while ref pred body = while'
 where
  while' = do
              v <- readIORef ref
              if (pred v)
                then body >> while'
                else return ()

{- ******************************* -}

import Data.IORef
import Control.Pascal

factorial n
 = do
      r <- newIORef 1
      i <- newIORef n
      while i (>0) (
        readIORef i >>= 
        modifyIORef r . (*) >>
        modifyIORef i ((+) (-1))
       )
      readIORef r

For instance:

Prelude> factorial 5
120