push item place → new-place-value

item — an object.

place — a place, the value of which may be any object.

new-place-value — a list (the new value of place).

push prepends item to the list that is stored in place, stores the resulting list in place, and returns the list.

For information about the evaluation of subforms of place, see Section 5.1.1.1 (Evaluation of Subforms to Places).

(setq llst '(nil)) → (NIL) 
(push 1 (car llst)) → (1) 
llst → ((1)) 
(push 1 (car llst)) → (1 1) 
llst → ((1 1)) 
(setq x '(a (b c) d)) → (A (B C) D) 
(push 5 (cadr x)) → (5 B C) 
x → (A (5 B C) D)

The contents of place are modified.

pop, pushnew, Section 5.1 (Generalized Reference)

The effect of (push item place) is equivalent to

(setf place (cons item place))

except that the subforms of place are evaluated only once, and item is evaluated before place.