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.
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