[Haskell-cafe] how to print out intermediate results in a recursive function?

Qi Qi qiqi789 at gmail.com
Sat Feb 4 19:23:07 CET 2012


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.

Qi Qi

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