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

Well, if you want that in production, not for debugging purposes, you should change the type signature of mergesort so that it uses some monad. Printing requires IO monad; however, I would advise to collect all intermediate results using Writer monad, and print them afterwards:

mergesort [] = return [] mergesort [x] = return [x] mergesort xs = do tell [xs] -- that's right, "[xs]", not "xs" let (as, bs) = splitAt (length xs `quot` 2) xs liftM2 merge (mergesort as) (mergesort bs) Also, don't forget that IO actions are values too. IOW, your list of intermediate results can be a list of IO actions, effectively deferring

On 04/02/2012 08:46, MigMit wrote: their "execution" until later.