On Thu, Dec 31, 2009 at 5:50 AM, Luke Palmer <lrpalmer@gmail.com> wrote:

Code looks okay. It suffers from the same persistence/amortization
problem as the classical functional queue; if you happen to shift from
one of the edge cases (eg. prev when the left is empty), you will get
degenerate time complexity, reversing that right list over and over.
See discussion at "Simple and efficient purely functional queues and
deques, by Chris Okasaki"; probably can adapt that solution to yours.
More of an academic interest, I doubt anyone will care about those
cases.

Yes. I agree and did see it. I'm reading the paper and may implement some of the stuff he talks about.

Ring is a comonad, so you can make it an instance of one if you want
to have some fun :-P

I plan on adding as many instances as I know and make sense to me. :)

It seems weird that you would put the focus in the middle in fromList.
Overly strict. Why not just put it at the first element? (Also
easier to reason about)

It actually uses the first element as the focus, not the middle.

I would consider considering a ring where *both* left and right were
infinite to be valid, but not when only one of them is infinite (when
they both are infinite, you will never get to reverse).

This would be neat, perhaps someday. I don't think this works well with my current API. :(