One reason might be that Jx's adverb O. expects a verb in tail-recursive form and bad things might happen if it is not and currently it cannot determine automatically if it is. Jx is not for the faint of heart and will stay there but I am not sure about J Unbox or the official interpreter.
On Mon, Mar 21, 2016 at 6:21 PM, Pascal Jasmin <[email protected]> wrote: > Can't think of a reason why we wouldn't want this in the official > interpreter > > > > > ----- Original Message ----- > From: Jose Mario Quintana <[email protected]> > To: Programming forum <[email protected]> > Sent: Monday, March 21, 2016 9:54 AM > Subject: Re: [Jprogramming] Tail recursion (bug hijack) > > Right, I never saw or found a satisfactory coding of a genuine while > conjunction. However, in Jx one can afford, thanks to Thomas' effective > implementation of the adverb O. for the Jx interpreter, to do the > unthinkable: code a genuine while conjunction recursively! That is, a > conjunction wTCO such that, > > u wTCO v > ]`($:^:(1:`u))@.v O. > > This is how it works for the case at hand, > > whileO =: v1@:(v0 wTCO (-. @: v2)) NB. > > power i.20 > 0 7 8 9 10 11 12 13 14 15 16 17 18 19 > recursive i.20 > 0 10 11 12 13 14 15 16 17 18 19 > whileO i.20 > 0 10 11 12 13 14 15 16 17 18 19 > recursiveO i.20 > 0 10 11 12 13 14 15 16 17 18 19 > > > stp=. ([ ((<;._1 '|Sentence|Space|Time|Space * Time') , (, */&.:>@:(1 > 2&{))@:(] ; 7!:2@:] ; 6!:2)&>) (10{a.) -.&a:@:(<;._2@,~) ]) ".@:('0 : > 0'"_) > > Y=. i.111 > > stp 11 > > recursive Y > whileO Y > recursiveO Y > ) > ┌──────────────┬──────┬────────────┬────────────┐ > │Sentence │Space │Time │Space * Time│ > ├──────────────┼──────┼────────────┼────────────┤ > │ recursive Y│222592│0.0475173844│10576.9896 │ > ├──────────────┼──────┼────────────┼────────────┤ > │ whileO Y│36992 │0.0397433474│1470.18591 │ > ├──────────────┼──────┼────────────┼────────────┤ > │ recursiveO Y│37376 │0.0434088376│1622.44871 │ > └──────────────┴──────┴────────────┴────────────┘ > > > On Sat, Mar 19, 2016 at 2:39 PM, Dan Bron <[email protected]> wrote: > > > Louis wrote: > > > The problem is that u^:v^:_ y terminates > > > either when 0 = v y OR when y -: u y . > > > > Yeah, this has bitten us all at one time or another. The traditional > > solution is to add a little tag to the data structure which you mutate > > (along with the normal processing) at every iteration. Most commonly we > > just do (u@:>@:{. ; -.&.>@:{:)^:v^:_ y ; 0 (adjusting the boxing logic > as > > needed). > > > > I asked for better alternatives than this a few years back [1], but we > > didn’t come up with anything compelling. > > > > -Dan > > > > [1] J Programming thread, “Limit limitation, Oct 2009: > > > > http://www.jsoftware.com/pipermail/programming/2009-October/016513.html > < > > http://www.jsoftware.com/pipermail/programming/2009-October/016513.html> > > ---------------------------------------------------------------------- > > 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
