[Haskell-cafe] how to print out intermediate results in a recursive function?
byorgey at seas.upenn.edu
Sat Feb 4 15:27:50 CET 2012
On Sat, Feb 04, 2012 at 12:23:07PM -0600, Qi Qi wrote:
> 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:
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