(import srfi-1)
(define a '(1 2 3 4 5 6))
(filter! even? a) ;; => (2 4 6)
a ;; expected (2 4 6), but got (1 2 4 6)
(define a '(1 2 3 4 5 6))
(filter even? a) ;; => (2 4 6)
a ;; => (1 2 3 4 5 6)