Simplified Common Lisp reference
Symbol class: Conses, Lists and related functions
Symbol type: macro
popplace => list
Argument description:
place a place containing list

POP macro modifies variable or generally place. It replaces the cons cell value with its cdr. Effectively it removes first element of the list found at the place. Result is the first element of the original list. See also PUSH, PUSH-NEW and ACONS.

(let ((x '(1 2 3))) (pop x)) => 1
(let ((x '(1 2 3))) (pop x) x) => (2 3)
(let ((x '((a b c) (3 2 1) (e f g)))) (pop (second x)) x) => ((A B C) (2 1) (E F G))
(let ((x '())) (pop x) x) => NIL
Function indexFull documentation for pop (HyperSpec)