title: How roughen (as opposed to flatten) a list in a functional style?
body: <p>For instance, I have a list <code>(1 2 3 4 5 6 7 8 9 10 11)</code>, and want to roughen it by 3 elements (or another length) to get <code>((1 2 3) (4 5 6) (7 8 9) (10 11))</code>. What pretty code could I use for this? Thanks.</p>