Question

Is there built in function or macro to append list to a mutable list. Something like PUSH, but slightly different.

Here is the PUSH using exapmle:

(setq v '(3))
(push '(1 2) v) ;v now ((1 2) 3)

And I need fallowing behavior:

(setq v '(3))
(mappend '(1 2) v) ;v should be (1 2 3)

Answer 1

I think you are looking for nconc?

[Function] nconc &rest lists

nconc takes lists as arguments. It returns a list that is the
arguments concatenated together. The arguments are changed rather than
copied. (Compare this with append, which copies arguments rather than
destroying them.) For example:

(setq x ‘(a b c)) (setq y ‘(d e f)) (nconc x y) => (a b c d e f) x
=> (a b c d e f)

You could use nconc to define a pushlist macro, to have an interface analogous to push:

(defmacro pushlist (lst place)
  `(setf ,place (nconc ,lst ,place)))

And test it:

CL-USER> 
(defparameter *v* (list 3))
*V*
(pushlist (list 1 2) *v*)
CL-USER> 
(1 2 3)
CL-USER>
*v*
(1 2 3)
CL-USER> 

Also note that I’m using (list 3), instead of ‘(3), after reading sigjuice’s comment.