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

[Ivan Lazar Miljenovic]

On 5 February 2012 05:23, Qi Qi <qiqi789 at gmail.com> wrote:
> Hello,
>
> I have a question;how can I print out the intermediate number lists in a
> mergesort recursive function like the following one.

You can use the (completely evil and shouldn't be used in production
code) Debug.Trace module.

>
> 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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-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com