On Fri, Feb 13, 2009 at 2:34 AM, Robert Bradshaw
<rober...@math.washington.edu> wrote:
>
> I have written up extensive documentation on the coercion model at
> http://wiki.sagemath.org/coercion . If you find coercion baffling,
> confusing, or unuseful, this is especially for you. I am sure there
> is lots of room for improvement, as what may be obvious to me can be
> far from obvious to those less familiar with the system. This is
> intended to be the guide to using coercion--for deeper implementation
> details see the docstrings in the coerce.pyx (100% coverage) and
> related files.
>
> Eventually, this should all be moved to the reference manual and/or
> programing guide, but I figured the wiki was the best place to put it
> at the moment. Comments welcome.
>
> - Robert
I was just looking at this from the context of implementing quaternion
algebras (again) using this framework. It's actually striking how
most of the code in Sage does not use the new coercion framework.
The vast majority of rings and other objects in Sage still use the old
framework. E.g., there are 88 uses of the deprecated _coerce_impl and
there are only about 12 uses of the new _populate_coercion_list
replacement. Because it hasn't got used so much in Sage, maybe the
new coercion model implementation probably has a lot of kinks to be
worked out, and people will likely run into these when trying to
implement classes that use it.
For example, I tried to get pickling of quaternion algebras to work --
and it won't if I use
self._populate_coercion_lists_(coerce_list=[base_ring])
in my code. It gave "weird errors" unless I comment it out, so I
checked around Sage (e.g., in free modules) for any other uses of this
pretty natural obvious use of populate_coercion_list in any deployed
code. There are 2 or 3 instances in all Sage of this. Not enough to
educate me.
Just out of curiosity, given a parent R and an element x, how do I
even do what used to be
R._coerce_impl(x)
i.e., do canonical coercion or give an error? The simplest thing I
could come up with is:
from sage.all import parent # horrid (since I'm lazy at the moment)
foo =R.convert_map_from(parent(x))
if not foo: raise TypeError
return foo(x)
Anyway the point of this email is that a cursory inspection suggests
that the new coercion model has only been pushed out to maybe 10% of
the parent structures in Sage. Is this true? Why isn't the rest
done? I feel like if (1) there were good documentation and (2) no
bugs (like the pickling issues I'm hitting), then it would be very
easy to push the new coercion model as you've designed it all over in
Sage. It was hell on earth last year to do that because people tried
to do everything at once. But given your superb evolutionary
approach, I think now it should be easy.
SUMMARY: I want coercion to get pushed throughout Sage, but I feel
like you need to write a very clear honest status report about what
the situation is now.
1. *Precisely* how much of the new coercion model has actually been
transitioned to in Sage now?
2. *Precisely* how much remains?
3. What's a list of 5 (say) parent structures where transitioning to
the new coercion model would be very easy?
William
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to sage-devel@googlegroups.com
To unsubscribe from this group, send email to
sage-devel-unsubscr...@googlegroups.com
For more options, visit this group at http://groups.google.com/group/sage-devel
URLs: http://www.sagemath.org
-~----------~----~----~----~------~----~------~--~---
