On Tue, Oct 18, 2011 at 05:04:10PM -0700, Alia wrote:
Ok, so having spent some further time on this. Methinks I have a solution below.
The aha moment occurred when I fell upon the definition of foldr and then looked at the recursive functions.
foldr :: (a -> b -> b) -> b -> [a] -> b foldr f z [] = z foldr f z (x:xs) = f x (foldr f z xs)
treeFold is implemented two ways, the first is as Brent advised, the second places the accumulator after the function and follows from foldr. I suspect the first approach is probably more practical because you can curry the accumulator away.
I don't think it makes a big difference which way you order the arguments. Since there is one argument for each constructor of Tree, I just like having the arguments in the same order as the constructors in the definition. But it's not really important.
It was a cool exercise in all. Thanks Brent! (-:
Glad you enjoyed it! Nicely done! -Brent