On Sat, Feb 04, 2012 at 12:23:07PM -0600, Qi Qi wrote:
Hello,
I have a question;how can I print out the intermediate number lists in a mergesort recursive function like the following one.
merge [] ys = ys merge xs [] = xs merge (x:xs) (y:ys) = if x <= y then x : merge xs (y:ys) else y : merge (x:xs) ys
mergesort [] = [] mergesort [x] = [x] mergesort xs = let (as, bs) = splitAt (length xs `quot` 2) xs in merge (mergesort as) (mergesort bs)
main = do print $ mergesort [5,4,3,2,1]
In the main function, it only prints out the final number list. But I'd like to print out the number lists in every recursive level. How can I do that? Thanks.
For visualizing intermediate steps for the purpose of debugging, there is also the very nice hood package: http://hackage.haskell.org/package/hood -Brent