On Tue, Nov 15, 2016 at 09:27:14AM +0100, Vincent Delecroix wrote: > On 15 November 2016 at 09:19, Thierry <sage-googlesu...@lma.metelu.net> wrote: > > On Tue, Nov 15, 2016 at 08:53:43AM +0100, Vincent Delecroix wrote: > >> Not currently (though we have "Unknown"). The main problem is the > >> interaction with Python booleans and the operators "or", "and", "not" > >> (which are *not* logical operators). The Sage "Unknown" is badly > >> broken for these reasons > >> > >> sage: not Unknown # waiting for Unknown > >> True > >> sage: Unknown or False # waiting for Unknown > >> False > >> > >> So be careful if you start using it! > >> > >> If we would use the correct logical operators ~ (for negation), ^ (for > >> xor) and & (for and) then we might be able to come up with something. > >> But Sage sort of ignore them. > >> > >> This problem has been discussed a lot on this mailing list and there > >> even exists a (refused) PEP request in this direction. > > > > For reference, it is https://www.python.org/dev/peps/pep-0335/ (the main > > reason for rejecting the proposal was "too much discussions"...). > > > > Perhaps was the proposal too greedy, so i wonder whether there would be a > > possibility to have a trool adding an Unknown to bool that does not > > perturb the speed when only True and False are used, and so that the > > "short-circuiting semantics" remains preserved. > > No way! In an expression such as > > "True or whatever_function(x)" > > the "whatever_function(x)" is *not* evaluated... > > sage: def f(): print "hello" > sage: True or f() > True
I do not see your point. True or Unknown should be True, right ? So we can shortcut here as well for trools, no ? Ciao, Thierry > > > This could indeed be useful in testing equality of overlaping > > real-intervals, undecidable problems in groups, equality of symbolic > > expressions, ... > > But I agree that it could be useful. > > Vincent > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To post to this group, send email to sage-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-devel. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
