CDR and CADR in this lisp

[sanrajbhar677632]

This is lisp programme to make selected object 's layer as current layer.

i used 1st cadr function (in place of CDR). it results some error. And then i used CDR . it works fine. can u tell me what is excat function of this two function. i supposed that cadr will be work well. please explain it


(DEFUN C:ES()
(SETQ A(CAR(ENTSEL "\Select Entity To current Layer..")))
(setq b(cdr (assoc 8(entget a))))
(command "-layer" "s" b ""))

[marko_ribar]

cdr - removes first element of a list and returns that list without first element

cadr = (car (cdr)) - removes first element of a list takes first element of resultant list (previously removed first element), so it basically means that cadr takes second element of a list and returns that element, because :

car - takes first element from a list and returns that first element

M.R.

[sanrajbhar677632]

so basically it wouldn't be error if cadrs are being used in this line (setq b(cdr (assoc 8(entget a)))) what u say ?

cdr - removes first element of a list and returns that list without first element

cadr = (car (cdr)) - removes first element of a list takes first element of resultant list (previously removed first element), so it basically means that cadr takes second element of a list and returns that element, because :

car - takes first element from a list and returns that first element

M.R.

[Lee Mac]

Have a read of this:

http://www.theswamp.org/index.php?to...2238#msg442238

[sanrajbhar677632]

Frnds, Please if i am some silly. dont mind. iam just learning it.

the below code is work well. can i know if entity is not get selected it should prompt No entity slected(without ending of programe).

This is lisp programme to make selected object 's layer as current layer.

i used 1st cadr function (in place of CDR). it results some error. And then i used CDR . it works fine. can u tell me what is excat function of this two function. i supposed that cadr will be work well. please explain it


(DEFUN C:ES()
(SETQ A(CAR(ENTSEL "\Select Entity To current Layer..")))
(setq b(cdr (assoc 8(entget a))))
(command "-layer" "s" b ""))

[Lee Mac]

The simplest solution could be:

(while (null (setq ent (car (entsel))))
    (princ "\nNothing Selected.")
)

[sanrajbhar677632]

great ! how to using "IF" Function

The simplest solution could be:

(while (null (setq ent (car (entsel))))
    (princ "\nNothing Selected.")
)

[sanrajbhar677632]

great ! how to using "IF" Function?

The simplest solution could be:

(while (null (setq ent (car (entsel))))
    (princ "\nNothing Selected.")
)

[Lee Mac]

(if (setq ent (car (entsel)))
    (expression_if_true)
    (princ "\nNothing Selected.")
)

[sanrajbhar677632]

It doesn't seems to works ?

(if (setq ent (car (entsel)))
    (expression_if_true)
    (princ "\nNothing Selected.")
)