OK, my last post on this tread for a while, I promise :). On Mar 11, 2009, at 7:19 PM, Bill Page wrote:
> On Wed, Mar 11, 2009 at 10:13 PM, David Roe wrote: >> On Wed, Mar 11, 2009 at 9:53 PM, Bill Page wrote: >>> >>> On Wed, Mar 11, 2009 at 9:08 PM, Carl Witty wrote: >>>> ... >>>> Does this mean you want GF(5)(3)*2 and RR(pi)*2 to fail? These >>>> currently work due to coercions that would be unsafe according >>>> to my >>>> definition. >>>> >>> >>> The __mul__ method exported by GF(5) could accept integers as >>> well as >>> elements of GF(5), i.e. rely on operator polymorphism rather than >>> non-strict coercion in such cases. >> >> The reason we have coercion is so that we don't have to do this. +10. Otherwise every element has huge if-else lists in every __add__, __sub__, __mul__, etc. corresponding to the fixed list various possibilities that the programer original programmer thought of at the time, and then those who've added to it. Much better to have a central system that one can reason with. Then the author of _mul_ only has to worry about how to actually multiply two elements of the same kind. And it makes it much messier to handle stuff like ZZ['x'] + 1/2. > I presume that you do not mean to imply that this is the only reason > to have coercion. Could it be said that this is the reason why you > want non-strict (unsafe) coercions? I see this as one of the primary motivations to have coercion at all, "safe" (injective?) or not. BTW > Here's some examples to hopefully clarify: > RealField(20) -> RealField(50) > RealField(20) -> RealIntervalField(20) I would call these dangerous, as the latter implicitly has more "information" than the former. - Robert --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
