Handy looping function

[Jeremy Dunn]

First the code:

Code Select Expand


(define (dolist-choice n A B C)
  (if (list? n)
      (setq n (dec (length n))))
  (eval (if C
           (if (zero? $idx) A (= $idx n) B C)
           (if (member $idx '(0 n)) A B)
        )
  )
)


This is a special branching function designed for being used within a DOLIST loop. The function can take up to 4 arguments. The first argument is either the list we are looping through or the integer value of the largest index of the list. If we supply a list then the largest index is found for us. A, B, C are each one or more program statements to be executed. If we have all three then if $idx is 0 A is executed else if $idx is the last index B is executed else if $idx is any other index then C is executed. If only A and B are present then if $idx is the first or last index A is executed else B is. I find this one very handy for the toolbox and it can really clean things up - enjoy!

[Kazimir Majorinc]

Code Select Expand

(dolist(i (sequence 0 9))
  (dolist-choice (sequence 0 9)
     '(println "first: " i)
     '(println "last: " i)
     '(println "inner: " i)))
(exit)

; first: 0
; inner: 1
; inner: 2
; inner: 3
; inner: 4
; inner: 5
; inner: 6
; inner: 7
; inner: 8
; last: 9

Nice.

[Kazimir Majorinc]

In general case we have (= $idx 0) for first, but we miss something like (= $idx $maxidx) for last repetition in loop. We don't have it, right? So, I'm proposing it. $maxidx cannot be known in while, until ... but it can in dotimes, dolist, dostring, for, doargs and map.

[Lutz]

In  (dotimes (s N) ...) it would be N. In 'dostring' it would be ambiguous, as only the memory food-print-size is stored, which may be different from the visible length (specially on UTF-8 versions). On all other, newLISP doesn't really know the size until walking through the whole list.