#;5> (define a '((foo . 1) (bar . 2)))
#;6> (define b (alist-update! 'baz 3 a))
#;7> a
((foo . 1) (bar . 2))
#;8> b
((baz . 3) (foo . 1) (bar . 2))
#;9> (define c (alist-update! 'baz 4 b))
#;10> a
((foo . 1) (bar . 2))
#;11> b
((baz . 4) (foo . 1) (bar . 2))
#;12> c
((baz . 4) (foo . 1) (bar . 2))