On Tue, May 20, 2014 at 11:50:30AM +0200, Vincent Delecroix wrote:
> I agree with Nathan that .sum must be changed. IMHO I would
> - remove sum from the element Composition
+1
> - move the sum from the category CommutativeAdditiveMonoids to AdditiveMagmas
With #10963 (which is merged!), sum has already been moved in
AdditiveMonoids. A version not using the zero (and supporting only non
empty lists) could possibly be added to AdditiveSemigroups. I am not
sure I want to define sum if the addition is not associative (for
multiplicative magmas, prod is only defined in the associative case).
> - Turn the parent Compositions into an additive monoid
>
> That way, the old behavior of sum can still be used through
> {{{
> sage: Compositions().sum([Composition([3,2,1]), Composition([1,2])])
> [3, 2, 1, 1, 2]
> }}}
+1. Or maybe instead into a multiplicative monoid? I don't have a
strong opinion either way, but we should take a consistent decision
here with words and other word-like objects supporting concatenation.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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