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
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 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