Michael: You can try creating a JIRA ticket suggesting that Clojure's = should return false when comparing floats and doubles to each other. I have no idea if it would go anywhere, but alternative (2) trying to get hashes to be equal between = float/doubles has been suggested and declined. Without some new convincing argument in favor of (2), it seems unlikely to change.
Another alternative might be an option to throw an exception if any floats creep into Clojure territory from Java, if that boundary line is even drawable. Andy On Fri, Jan 23, 2015 at 4:45 AM, Michael Gardner <gardne...@gmail.com> wrote: > I'm sure we are all aware of the various issues with floating point math > (particularly equality comparisons); however none of that is relevant to > this discussion. The only issue here is an inconsistency between hashing > and equality testing in Clojure. > > My claim is that the property "any two objects can be equal only if their > hashes are equal" is a fundamental one that should not be violated under > any circumstances. Whether that means modifying Clojure's hashing algorithm > or its implementation of = doesn't much matter to me, so long as that > property is maintained. > > > On Jan 23, 2015, at 5:06 AM, Luc Préfontaine < > lprefonta...@softaddicts.ca> wrote: > > > > Well if it breaks elsewhere than in your code because you mix > representations and leak > > them to some library in Java that you do not control I see my comments > as absolutely relevant. > > > > It's not technical, it's failsafe. But that might not be of any interest > to your problem scope. > > However it does interest me. Hiding odd behaviors when consistency can > be guaranteed, > > I have no problem with that. Here to me its very clear that there is no > failsafe approach. > > > > Clojure is hosted on a platform that does not provide the kind if > consistency you want. > > Anything you can build to hide this in Clojure is like building a tower > on moving sand. > > > > Mark has a valid point about type safety which helps a bit in Java but > you can dig > > with google and you will find people that got bitten in Java by > float/double mixing > > even with type 'safety'. So long for type systems, it cannot help you > with values that > > 'look' the same superficially but are internally different. > > > > For some values, floats and doubles are equal because their internal > representations are the > > same. For many other values it's not working. > > > > I suggest some readings; > > > > http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html > > http://floating-point-gui.de/errors/comparison/ > > > > Then maybe we can bring this thread to an end. > > > > > >> If there's a technical reason why Clojure can't return false for all = > comparisons between floats and doubles, I'd like to hear it. Otherwise, I > don't see how your response is relevant. > >> > >>> On Jan 23, 2015, at 3:10 AM, Luc Prefontaine < > lprefonta...@softaddicts.ca> wrote: > >>> > >>> Agree, it's broken... in java... > >>> Has it has been broken in the past in several architectures... > >>> > >>> I understand your frustration but this is not something new. It's been > a problem for at least 30 years. > >>> > >>> It is kind of a basic programming issue: > >>> > >>> - Never compare floats with different representations. > >>> > >>> - Never mix different representations in computations > >>> > >>> - Convert representations as early as possible to a common format > >>> > >>> These are the rules to follow to avoid running into trouble. > >>> > >>> Now if you think you can overcome this persistent (ah ! ah !) problem > with some David Copperfield trick, fine. > >>> > >>> But that's a trick nothing else. The problem will resurface in some > form in another. Better cope with reality... > >>> > >>> Luc P. > >>> > >>> > >>>> On Jan 23, 2015, at 1:33 AM, Immo Heikkinen <immo.heikki...@gmail.com> > wrote: > >>>>> > >>>>> I actually ran into this while comparing nested data structures from > two different sources and spent a good part of my day figuring out what's > happening. While it is a good advice to avoid mixing floats and doubles, it > is inevitable that Clojure users will get bitten by this once in a while > and hours will be wasted. > >>>>> > >>>>> It is also very disturbing to realise that "(= a b)" doesn't always > imply "(= (hash a) (hash b))" or "(= #{a} #{b})" as you would think. > >>>> > >>>> (inc) > >>>> > >>>> This is fundamentally broken behavior. Telling people to just learn > to avoid it is not good, IMO. If the hashes must be unequal, then = should > return false. > >>>> > >>>> As for backwards compatibility, note that if such a change were made > to =, it wouldn't affect anyone who was already following Andy's advice to > avoid mixing doubles and floats. IOW, it should only affect those who are > doing something you're not "supposed" to do anyway. > >>>> > >>>> -- > >>>> You received this message because you are subscribed to the Google > >>>> Groups "Clojure" group. > >>>> To post to this group, send email to clojure@googlegroups.com > >>>> Note that posts from new members are moderated - please be patient > with your first post. > >>>> To unsubscribe from this group, send email to > >>>> clojure+unsubscr...@googlegroups.com > >>>> For more options, visit this group at > >>>> http://groups.google.com/group/clojure?hl=en > >>>> --- > >>>> You received this message because you are subscribed to the Google > Groups "Clojure" group. > >>>> To unsubscribe from this group and stop receiving emails from it, > send an email to clojure+unsubscr...@googlegroups.com. > >>>> For more options, visit https://groups.google.com/d/optout. > >>>> > >>> -- > >>> Luc Prefontaine<lprefonta...@softaddicts.ca> sent by ibisMail! > >>> > >>> -- > >>> You received this message because you are subscribed to the Google > >>> Groups "Clojure" group. > >>> To post to this group, send email to clojure@googlegroups.com > >>> Note that posts from new members are moderated - please be patient > with your first post. > >>> To unsubscribe from this group, send email to > >>> clojure+unsubscr...@googlegroups.com > >>> For more options, visit this group at > >>> http://groups.google.com/group/clojure?hl=en > >>> --- > >>> You received this message because you are subscribed to the Google > Groups "Clojure" group. > >>> To unsubscribe from this group and stop receiving emails from it, send > an email to clojure+unsubscr...@googlegroups.com. > >>> For more options, visit https://groups.google.com/d/optout. > >> > >> -- > >> You received this message because you are subscribed to the Google > >> Groups "Clojure" group. > >> To post to this group, send email to clojure@googlegroups.com > >> Note that posts from new members are moderated - please be patient with > your first post. > >> To unsubscribe from this group, send email to > >> clojure+unsubscr...@googlegroups.com > >> For more options, visit this group at > >> http://groups.google.com/group/clojure?hl=en > >> --- > >> You received this message because you are subscribed to the Google > Groups "Clojure" group. > >> To unsubscribe from this group and stop receiving emails from it, send > an email to clojure+unsubscr...@googlegroups.com. > >> For more options, visit https://groups.google.com/d/optout. > >> > > -- > > Luc Préfontaine<lprefonta...@softaddicts.ca> sent by ibisMail! > > > > -- > > You received this message because you are subscribed to the Google > > Groups "Clojure" group. > > To post to this group, send email to clojure@googlegroups.com > > Note that posts from new members are moderated - please be patient with > your first post. > > To unsubscribe from this group, send email to > > clojure+unsubscr...@googlegroups.com > > For more options, visit this group at > > http://groups.google.com/group/clojure?hl=en > > --- > > You received this message because you are subscribed to the Google > Groups "Clojure" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to clojure+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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