flatten in scheme

;; Here ya go. This is flatten in scheme.
;; Has a nasty little thing in that it flattens improper lists to proper lists
;; but at least it won't die.
(define (flatten lst)
  (let loop ((lst lst) (acc '()))
    (cond
     ((null? lst) acc)
     ((pair? lst) (loop (car lst) (loop (cdr lst) acc)))
     (else (cons lst acc)))))