Point taken. But neither you nor I (for example) have bothered to be interested enough in Red Black trees to implement anything better. And for a problem that size, it's really not right to put an hour into criticizing it when an hour could have been used to show what you mean using an actual implementation.
And when you have a working implementation to test against, and a simple specification like that, if it takes longer than an hour for someone familiar with J to implement something better is it really fair to call that approach "better"? Thanks, -- Raul On Mon, Sep 8, 2014 at 7:06 PM, Dan Bron <j...@bron.us> wrote: > Yes, but to Devon's point, having a direct transliteration of an algorithm > originally expressed in a (very) different language doesn't tell us anything > about J's power (or not) to express that algorithm. > > Any programming language worth discussing is Turing complete. Which means > they're all *capable* of expressing anything computable (which means anything > you, a human, could do with a sufficient supply of paper, pencils, and time). > Each can express anything any of the others can express. > > So asking "can J express X?" isn't the interesting question (the answer is > "yes"). The interesting question is: what does J make it *simple* to express? > And, by implication (because several of the most fundamental theories humans > have developed to date, and all of human experience prior to that, tell us > that every decision is a tradeoff, and every benefit comes at a cost), what > does it make harder to express? > > You will note that Thomas' excellent contribution achieves its practical > results by implementing a stack language (that is, another programming > language) inside of J. > > -Dan > > PS: It's worth pointing out that you yourself (Raul) have drawn the > distinction between "doable, practically speaking" and "convenient" (or may I > say, "elegant"?) in your proposed enhancements to FSM (dyad ;:): > > http://www.jsoftware.com/pipermail/chat/2014-January/005653.html > > And, for whatever it's worth, I agree with you: > > http://www.jsoftware.com/pipermail/general/2005-September/024446.html > > Please excuse typos; sent from a phone. > >> On Sep 8, 2014, at 6:37 PM, Raul Miller <rauldmil...@gmail.com> wrote: >> >> It is, nevertheless, an implementation. >> >> And anyone that feels like doing so can supply other alternates (or >> replace it, if they feel theirs is good enough). >> >> Thanks, >> >> -- >> Raul >> >> >>> On Mon, Sep 8, 2014 at 5:28 PM, Devon McCormick <devon...@gmail.com> wrote: >>> This looks like a transliteration from another language - not J-like at >>> all. Once clue is that it's several times as long as many of the other >>> implementations. >>> >>> >>>> On Mon, Sep 8, 2014 at 4:05 PM, Joe Bogner <joebog...@gmail.com> wrote: >>>> >>>> I found an implementation of red-black trees on rosettacode: >>>> http://rosettacode.org/wiki/Pattern_matching#J ... It might be relevant >>>> or >>>> may not be. >>>> >>>> On Mon, Sep 8, 2014 at 3:45 PM, Devon McCormick <devon...@gmail.com> >>>> wrote: >>>> >>>>> A little research clarified what we see here: apparently it's part of the >>>>> definition of a binary tree that the left node be smaller than its parent >>>>> but the right one is greater. Right away, I see a problem for the >>>>> predecessor-index representation of a tree that I'm advocating as it does >>>>> not distinguish between right and left nodes as it is usually >>>> implemented. >>>>> >>>>> >>>>> On Mon, Sep 8, 2014 at 3:03 PM, Devon McCormick <devon...@gmail.com> >>>>> wrote: >>>>> >>>>>> Do you have a reference to a good example of this? Looking at the >>>>>> "before" and "after" pictures on the right here - >>>>>> http://en.wikipedia.org/wiki/Self-balancing_binary_search_tree - the >>>>>> rebalancing seems arbitrary as it preserves some relations but changes >>>>>> others. >>>>>> >>>>>> >>>>>>> On Mon, Sep 8, 2014 at 2:30 PM, Dan Bron <j...@bron.us> wrote: >>>>>>> >>>>>>> Raul wrote: >>>>>>>> Note that J already supports trees. >>>>>>> >>>>>>> Devon wrote: >>>>>>>> I have J code that uses trees which I run daily and >>>>>>>> have been doing so for years. >>>>>>> >>>>>>> Pascal wrote: >>>>>>>> I think trees are done at least ok, if not "right" already. >>>>>>> >>>>>>> Challenge: express, in J, the logic of rebalancing a heap (say, a >>>>>>> Fibonacci >>>>>>> heap, but I'm not particularly picky). >>>>>>> >>>>>>> For the sake of this exercise, you may ignore considerations of >>>>> efficiency >>>>>>> (though that's a bit of a self-contradiction, because heaps are >>>>> frequently >>>>>>> introduced specifically for the sake of efficiency). I am only >>>>> interested >>>>>>> in the directness, simplicity, elegance (lyricality) of the notation, >>>> in >>>>>>> its current form, for expressing ideas about trees. We can make it >>>>>>> efficient "later" (Pepe's TCO utility is a start). >>>>>>> >>>>>>> -Dan >>>>>>> >>>>>>> >>>>>>> >>>>>>> ---------------------------------------------------------------------- >>>>>>> For information about J forums see >>>> http://www.jsoftware.com/forums.htm >>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> Devon McCormick, CFA >>>>> >>>>> >>>>> -- >>>>> Devon McCormick, CFA >>>>> ---------------------------------------------------------------------- >>>>> For information about J forums see http://www.jsoftware.com/forums.htm >>>> ---------------------------------------------------------------------- >>>> For information about J forums see http://www.jsoftware.com/forums.htm >>> >>> >>> >>> -- >>> Devon McCormick, CFA >>> ---------------------------------------------------------------------- >>> For information about J forums see http://www.jsoftware.com/forums.htm >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
