If a selection has values

[My_Civil_3D]

Hi guys i need some help.

I am trying to make a lisp that if a selection set has items in it, it needs to do "this" otherwise do "that".

My Code:

(defun c:foo (/)
(setq xr(ssget "x" '((0 . "INSERT")(8 . "..TEST"))))
(setq xrnum (sslength xr))

 The Next part i need help with not sure how to do the if  argument if there are values or not:

(cond

         ((= xrnum nil)  <---- CANT GET THIS RIGHT not sure how to do the contains nothing or contains something

          (do "this")

          ))

[Automohan]

You didn't mention that what you need to do !

[Kent1Cooper · Accepted solution]

You can check it right in the process of getting the selection:

(defun c:foo (/ xr xrnum)
  (if (setq xr (ssget "x" '((0 . "INSERT")(8 . "..TEST"))))
    (repeat (setq xrnum (sslength xr)) ;; then
      (... do ... "this" ...) ;; [assuming doing something to all selected]
    ); repeat
    (... do ... "that" ...) ;; else
  ); if
  ....

because (ssget) will return nil if there are no objects found that fit the filter list criteria.  If "this" is something collective that can be done to the entire selection [for example, changing them all to a certain Layer, assuming they're all in the current space], and doesn't involve doing something to each object found independently, it's simpler:

(defun c:foo (/ xr xrnum)
  (if (setq xr (ssget "x" '((0 . "INSERT") (8 . "..TEST"))))
    (... do ... "this" ...) ;; then
    (... do ... "that" ...) ;; else
  ); if
  ....

[john.kaulB9QW2]

You are creating a boolean conditional construct and instead of using:

(if (setq xr (ssget "x" ...

you should create a "Boolean variable" to help construct a conditional.

(setq selectionsset (ssget "x" '((0 . "INSERT")) ...
(if selectionset ...

When creating a `Boolean variable` you should use positive variable names.
Examples:
full
ready
etc.

Using negative verbs results in confusing code like:
(if (not notfull) ...
(if (not notReady) ...

This keeps code more readable and straight forward (less confusing) and often times people assume the smaller number of lines of code the better it is but that isn't the case. The cleaner the code the better, and sometimes that means creating a variable to offer up more coherent code (for *OUR* readability included).

[ronjonp]

@My_Civil_3D It's also beneficial to read the online HELP.