I have a few questions about destructive functions. Can anybody explain why setf doesn't work with passed values ? It may return correct value, but it doesn't change the variable itself.
PS maybe it would be better if I describe full problem:
I need to edit branches or / and leafs inside a tree. I wanted to pas the branch as a parameter to my changing function, and process it with destructive pop and push functions, but it doesn't work. Is there a right way to do this?
It works for local variables
14
9
What exactly do you dislike?
It doesn't work with passed values.
(define (destruct lst) (setf (lst 3 0) 1))
(destruct x)
-> 1
This won't change the variable.
According to the manual,
//http://www.newlisp.org/downloads/newlisp_manual.html#pass_big
Quote
Variable's
Then
And according to the same chapter in manual.
//http://www.newlisp.org/downloads/newlisp_manual.html#pass_big
Quote
For example:
> (set 'y:y '(0 1 2 (3 4)))
(0 1 2 (3 4))
> (define (destruct lst) (setf (lst 3 0) 1))
(lambda (lst) (setf (lst 3 0) 1))
> y:y
(0 1 2 (3 4))
> (destruct y)
1
> y:y
(0 1 2 (1 4))
>
Note that there is no quote before
Without using contexts, demonstrated by johu, if you want
(set 'x '(0 1 2 (3 4)))
(define (destruct lst) (setf (
(println x)
(setf (x 3 0) 4)
(println x)
(destruct 'x)
(println x)
Another way for dereference (if you want to do it once in larger blocks) is
(letex((lst lst))
(setf (lst 3 0 0) 1)
(setf (lst 3 0 1) 2)))
Thank you fro the answers, that solved the problem.