Talk of uniqueness and so forth on the various Haskell mailing lists  
causes me to wonder: with so much imperative code being written in  
Haskell these days, to what extent is / should GHC perform standard  
imperative optimizations?  A few things come to mind:
   - Fetch elimination for imperative reads:
     writeIORef r e >> acts >> readIORef r === writeIORef r e >> acts  
 >> return e
     readIORef r >>= \e -> acts >> readIORef r ===
	readIORef r >>= \e -> acts >> return e
     And that sort of thing, generalized for other imperative monadic  
types...
     My feeling is this doesn't come up much in code as written on  
the page,
     but might well be relevant after inlining.
   - Some way to turn the following idiom into memcpy (for any array  
type):
     do a <- newArray
        writeArray a 0 e0
        writeArray a 1 e1
        writeArray a 2 e2
        ...etc...

What say others?  Is there a need yet?  (I don't honestly know the  
answer!)

-Jan-Willem Maessen