On Mon, 6 Dec 2010 16:30:10 -0500
Ken Wesson <kwess...@gmail.com> wrote:
> On Mon, Dec 6, 2010 at 1:05 PM, Stuart Sierra
> <the.stuart.sie...@gmail.com> wrote:
> > On Dec 6, 8:36 am, Ken Wesson <kwess...@gmail.com> wrote:
> >> Furthermore, the comment (not made by Hickey) that map order "may be
> >> unstable" is more than a little puzzling in light of the fact that the
> >> maps in question are immutable. :)
> >
> > In general, Rich has been careful not to promise things that might
> > limit changes he can make in the future. Sets and maps are unordered.
> > `seq` happens to be deterministic on ArrayMap and HashMap, but there
> > might some day be some other kind of map or set for which `seq` cannot
> > be deterministic. Therefore, Clojure does not promise anything about
> > `seq` on maps, other than that it will return the key-value pairs.
>
> I confess I can't see any obvious reason ever to make seq
> nondeterministic on an immutable data structure.
I suspect you're applying "immutable" to everything about the data
structure, whereas it can also be applied the value without including
the implementation. I can see wanting to change the implementation in
ways that don't change the value - triggered by something like wanting
to share parts of the value with another structure, or a garbage
collection, or ... - which could easily change the results of calling
seq on the structure.
Not that I know that anything in clojure does that, just that I can
see conditions where you might want to.
<mike
--
Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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