On Sat, Jan 31, 2015 at 10:39 PM, YCH <dontdieych@gmail.com> wrote:
        ys' = groupByN ys n
            where
                groupByN [] _ = []
                groupByN zs m = take m zs : groupByN (drop m zs) m

This groupByN doesn't look like it'll terminate for negative n. So ys' becomes an infinite list. Which causes divergence downstream.

-- Kim-Ee