Perhaps this Vocabulary entry for Memo M. will help http://www.jsoftware.com/docs/help701/dictionary/dmcapdot.htm
There is also Self Reference $: http://www.jsoftware.com/docs/help701/dictionary/dmcapdot.htm Kip Murray Sent from my iPad On Feb 11, 2013, at 7:04 AM, Alex Giannakopoulos <[email protected]> wrote: > Are there any resources on recursive programming in J? Couldn't find much > by searching. > I would particularly like to know about scoping, and also so-called free > variables. > > It seems to me that the enforced naming of variables as 'x' and 'y' might > cause problems in nested functions, necessitating awkward renaming and > copying. > > I will give a little example here (my apologies to those unfamiliar with > Scheme.) > I am trying to write a routine that will return ALL the factors of a > number, not just the prime ones. > I do this by using an auxiliary routine that takes the number to factor and > a list of numbers still to combine. > > ;; function (unique numlist) corresponds to J's ~. > ;; function (remel alist elem) corresponds to J's [ }.~ [: >: i. > ;; function (primefactors n) corresponds to J's q: > > (define (allfactors n) (af n (primefators n)) > > (define (af num divisors) > (if (null? divisors) (list num) > (let ((uniquefactors (unique divisors))) > (flatten > (cons num > (map (lambda(x) (af (/ num x) (remel divisors x))) > uniquefactors)))))) > > Now I tried to express this in J, but can't even get to first base, because > of the scoping problems I mentioned. > I realise that recursion is not the primary mode for programming J, and a > good solution may instead use something like running totals (\), but for > the time being I am stuck. > Any suggestions gratefully received. > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
