multiple methods pattern bug(?)

[Ch. A. Herrmann]

Hi,

the following instance declaration doesn't work any
more with ghc-5.02.3, it worked before.

> newtype ST state a = ST { unST :: state -> (a,state) }
> 
> instance Monad (ST c) where
>  return x  = ST (\state -> (x,state))  
> (m >>= f) = ST (\state -> let (x,state1) = unST m state
>                               (y,state2) = unST (f x) state1
>                           in (y,state2)) 

Error message:
    Can't handle multiple methods defined by one pattern binding
	(m >>= f)
	    = ST (\ state
		      -> let
			   (y, state2) = ...
			   (x, state1) = ...
			 in (y, state2))

What can I do instead?

--
 Christoph