cycling commands do not go backward

[Samuel Wales <samologist@gmail.com>]

A philosophical note.

Many commands in emacs cycle or rotate or go forward in a list.
Examples include the mark ring, the global mark ring, undo,
hippie-expand, dabbrev-expand, and other completion mechanisms.

Yet most of those commands do not cycle backward.  That is, if you
overshoot, you have to do a lot more cycling to get around to the
previous completion (or whatever).  In the case of undo, it is more
complicated than a ring, but the problem is the same.  You can undo,
but if you overshoot, you are often better off giving up.  (If you
think that the existing mechanisms are sufficient, take a look at the
previous discussions of this on this list and on wikis to find out
whey that is not correct.)

I suspect that this is because it is slightly easier to code it one way.
But for the user it would be great to be able to go both ways.

Consider the right arrow.  It has a complementary left arrow.
Perhaps, as a user interface design goal, the same idea can be applied
to cycling and rotating commands, and to undo.

-- 
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