topic Better way to define constant symbol? in Visual LISP, AutoLISP and General Customization Forum

Better way to define constant symbol?

mmitchellH6TRW — Wed, 29 Jan 2020 19:01:46 GMT

I looking for a better way to define a constant symbol, so that it evaluates when used.

Currently:

(setq rot pi)
....
  (setq BKROT (quote (and (> rot (* pi 0.5)) (<= rot (* pi 1.5))))) ; define constant for Back Rotation
....
 (cond
	       ((eval BKROT) (something happens))
.....
(cond
	       ((not (eval BKROT)) (something happens))
......

;; what I would like

(setmagic BKROT (quote (and (> rot (* pi 0.5)) (<= rot (* pi 1.5))))) ; define self evaluating constant
.....
 (cond ( BKROT (something happens)) .....

Re: Better way to define constant symbol?

CodeDing — Wed, 29 Jan 2020 19:27:59 GMT

@mmitchellH6TRW ,

Then just perform the evaluation..?

(setq BKROT (and (> rot (* pi 0.5)) (<= rot (* pi 1.5))))
.....
(cond (BKROT (something happens)) .....

Best,

~DD

Re: Better way to define constant symbol?

ronjonp — Wed, 29 Jan 2020 21:55:52 GMT

Are you talking about defining a function to pass a rotation argument to?

(defun _mycheck (rot) (<= (/ pi 2) rot (* pi 1.5)))
(if (_mycheck (getangle)) (alert "YES :)")(alert "NO :("))

Re: Better way to define constant symbol?

Kent1Cooper — Thu, 30 Jan 2020 00:30:13 GMT

I'm trying to picture what the (quote) function is doing for you. The (and) function that it is applied to will return either T [with the value of pi at the beginning] or nil, so BKROT is going to be set to either (quote T) or (quote nil). I'm not at an AutoCAD to try, but I'm wondering what those do -- whether they even have any meaning....

Re: Better way to define constant symbol?

CodeDing — Thu, 30 Jan 2020 13:27:04 GMT

@mmitchellH6TRW ,

I think I know what you're going for, and this is as close as I can get. You have to call it as a function though [with brackets (...) ]. I'm not sure how to run the expression if you were to just call the symbol without brackets.

Is this more-so what you're looking for?

.....
(setq rot pi)
(setq BKROT (lambda () (and (> rot (* pi 0.5)) (<= rot (* pi 1.5))))) ; define constant for Back Rotation
(cond ((BKROT) (something happens)) .....
(setq rot 0.0)
(cond ((not (BKROT)) (something ELSE happens)) .....
.....

Best,

~DD

Re: Better way to define constant symbol?

mmitchellH6TRW — Thu, 30 Jan 2020 18:26:44 GMT

  (setq TAU (* pi 2))
  (setq BKROT (lambda () (and (> rot (* TAU 0.25)) (<= rot (* TAU 0.75))))) ; define constant for Back Rotation

is a condition to test of rot is on the back side of a circle. So later in the code I can call the condition....

	     (cond
	       ((BKROT) (cons 50 (+ rot pi (cdr (assoc 50 x))))) ; insertion angle on back side
	       (T (cons 50 (+ rot (cdr (assoc 50 x)))))	    ; insertion angle on front side
	     )						    ; (cond

as part of my entmake . The (assoc 50 x) pulls the insert angle from the original block. i.e. https://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/trying-to-entmake-a-block-insert-with-attributes/m-p/9280184/highlight/true#

	     (cond
	       ((BKROT) (cons 72 2))		    	    ; Horz 0 = Left; 1= Center; 2 = Right
	       (T (cons 72 0))				    ; Horz 0 = Left; 1= Center; 2 = Right
	     )						    ; (cond

Eight different calls to place blocks.

Re: Better way to define constant symbol?

CodeDing — Thu, 30 Jan 2020 19:23:00 GMT

@mmitchellH6TRW ,

Not to interrupt your flow or anything, but perhaps some simple 'improvements'?

(cond
  ((BKROT) (cons 50 (+ rot pi (cdr (assoc 50 x))))) ; insertion angle on back side
  (T (cons 50 (+ rot (cdr (assoc 50 x)))))	    ; insertion angle on front side
)
...to...
(cons 50 (+ rot (if (BKROT) pi 0.0) (cdr (assoc 50 x))))

(cond
  ((BKROT) (cons 72 2))	; Horz 0 = Left; 1= Center; 2 = Right
  (T (cons 72 0))	; Horz 0 = Left; 1= Center; 2 = Right
)
...to...
(cons 72 (if (BKROT) 2 0))

Best,

~DD

Re: Better way to define constant symbol?

mmitchellH6TRW — Thu, 30 Jan 2020 19:44:13 GMT

Thank you DD.

I see how you did that.

Thank you,

Mark