#18756: Use coerce actions in the category framework
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Reporter: SimonKing | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.8
Component: coercion | Resolution:
Keywords: cython, coercion, | Merged in:
actions, categories | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | e1111c346a82639bb41161469754d45008117801
u/SimonKing/combinatorial_free_module_cython_coercion| Stopgaps:
Dependencies: |
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Comment (by SimonKing):
Today I had a discussion with Nicolas, and the plan now is to connect
category and action framework more tightly.
To define an action of G on S, either `S._get_action_(G, op,
self_on_left=...)` should return an action (which is not an action in the
mathematical sense; it is just something that is callable on a pair of
elements) or `G._get_action_(S,op,self_on_left=...)` should return
something.
It would be good to make it easier for the category framework to override
that method. But methods inherited from Parent have precedence over
!ParentMethods. Hence, `Parent._get_action_` (which just returns None)
should be moved to `Sets.ParentMethods._get_action_`. Concrete parents can
still override _get_action_, and sub-categories could override it as well.
In addition to that, `Magmas.ParentMethods.__init_extra__` could use
`Parent.register_action` to register actions.
However, all that would require that actions of a parent on ITSELF are
possible. I guess technically they are possible. However,
`ModuleElement.__mul__` would refuse to use them: It raises an error, if
both elements have the same parents, which means that a ring structure can
really only be implemented by either inheriting from Element and providing
a custom `__mul__`, or by inheriting from !RingElement.
The framework for "actions on self" should be provided on a new ticket.
--
Ticket URL: <http://trac.sagemath.org/ticket/18756#comment:18>
Sage <http://www.sagemath.org>
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