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

[yi huang]

You can use trace from Debug.Trace, change the code like this:

mergesort l = case trace l l of
    [] -> ...
    [x] -> ...
    (x:xs) -> ...

On Sun, Feb 5, 2012 at 2:23 AM, 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.
>
> 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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-- 
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