Daniel Fischer wrote:
A simple way to check for sanity of the results is:
Prelude> :t flip foldr 0 . flip. curry flip foldr 0 . flip. curry :: (Num c) => ((c, b) -> c) -> [b] -> c
Prelude> :t \f list -> foldr (\x y -> f (y,x)) 0 list \f list -> foldr (\x y -> f (y,x)) 0 list :: (Num b) => ((b, a) -> b) -> [a] -> b
Prelude> :t \f -> foldr (uncurry $ flip f) 0 \f -> foldr (uncurry $ flip f) 0 :: (Num b1) => (b -> a -> b1 -> b1) -> [(a, b)] -> b1
So you see that your result has the correct type, while Hal's hasn't.
Can anyone figure out what Hal is up to, or does it look like a simple mistake?
Simple mistake. YAHT was never systematically proofread to catch all such mistakes, so there are several still in. Nevertheless, it is an excellent tutorial.
Thanks for the information, glad to know I was correct. I agree that YAHT is excellent... I am working from several books and tutorials simultaneously to get various perspectives, and YAHT covers much of the same material as the books, but in a more compact form, with good exercises. -Mike