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 > 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.
