On 19/08/2010, at 19:38, Johan Tibell wrote:

> Hi all,
>
> I tried doing the "standard" worker/wrapper transform to some functions in Data.Map. For example, by transforming
>
>     insertWith' :: Ord k => (a -> a -> a) -> k -> a -> Map k a -> Map k a
>     insertWith' f k x m
>       = insertWithKey' (\_ x' y' -> f x' y') k x m
>
>     -- | Same as 'insertWithKey', but the combining function is applied strictly.
>     insertWithKey' :: Ord k => (k -> a -> a -> a) -> k -> a -> Map k a -> Map k a
>     insertWithKey' f kx x t0
>       = case t of
>           Tip -> singleton kx $! x
>           Bin sy ky y l r
>               -> case compare kx ky of
>                    LT -> balance ky y (insertWithKey' f kx x l) r
>                    GT -> balance ky y l (insertWithKey' f kx x r)
>                    EQ -> let x' = f kx x y in seq x' (Bin sy kx x' l r)

Out of curiosity, is balance strict in the third argument? If not, does it make a difference if you make it strict?