Topic: Question on using APPLY

[Jeremy]

I was trying to use APPLY on DEFUN to see if I could create a function by passing the elements in a list. Something along the lines of

(apply 'defun (list 'mytestfunc nil (princ "it works!")))

But if I try to run this it does not create MYTESTFUNC. How can one get this to work if at all?

[alanjt]

Use LAMBDA or...

Code: [Select]

(eval (list 'defun 'mytestfunc nil (princ "it works!")))
What is the point of this?

[gile]

Hi,

Code - Auto/Visual Lisp: [Select]

1. (eval (cons 'defun (list 'mytestfunc nil '(princ "it works!"))))

Code - Auto/Visual Lisp: [Select]

1. (setq mytestfunc (lambda () (princ "it works!")))

<EDIT> Oops, too slow...

[JohnK]

*excited* ...I know this one.

I had this from way back.

Code - Auto/Visual Lisp: [Select]

1. (defun hook (func)
2.   ;; hook
3.   ;;
4.   ;; this function will take an argument and turn it into a
5.   ;; lambda expression to evaluate. (You can assign to a variable
6.   ;; and exec it at a later time if you wish.)
7.   ;;
8.   ;; Ex: (hook '(+ 1 2))
9.   ;;     > ((LAMBDA nil (+ 1 2)))
10.   ;;    
11.   ;; Ex 2: (setq zoom
12.   ;;            (hook '(vla-zoomextents
13.   ;;                (vlax-get-acad-object))))
14.   ;;     > ((LAMBDA nil (vla-ZoomExtents (vlax-get-acad-object))))
15.   ;;
16.   ;; By: John K
17.   ;;    (inspired by something I saw in one of
18.   ;;     Vladimir Nesterovsky's procedures.)
19.   ;;
20.   (list (cons 'lambda (cons nil (list func)))) )

[Jeremy]

Once again the answer is the root of all EVAL . So why is APPLY not sufficient? Is it not evaluating the function as is? Thanx for all the responses by the way.

[Lee Mac]

So why is APPLY not sufficient? Is it not evaluating the function as is?

Certain functions (usually Special Forms such as cond / foreach / defun etc.) cannot be evaluated using apply due to the difference in the way in which their arguments are evaluated.