Petite Chez Scheme Version 9.5
Copyright 1984-2017 Cisco Systems, Inc.

> (define a '(2 3 4))
> a
(2 3 4)
> (define b (cons 1 a))
> b
(1 2 3 4)
> a
(2 3 4)
> (define c '(2 3 4))
> (equal? a c)
#t
> (eq? a c)
#f
> (define fact
  (lambda (n)
    (cond [(zero? n) 1]
	  [else (* n (fact (- n 1)))])))
> (fact 4)
24
> (fact -2)
  C-c C-c
break>q break>q
Invalid command.  Type ? for options.
br(define fact2
  (lambda (n)
    (if (or (negative? n) (not (integer? n)))
	"error"
	(fact-acc n 1))))eak> q
> (define fact2
  (lambda (n)
    (if (or (negative? n) (not (integer? n)))
	"error"
	(fact-acc n 1))))
> (define fact-acc
  (lambda (n acc)
    (if (zero? n)
	acc
	(fact-acc (- n 1) (* n acc)))))
> (trace fact fact2 fact-acc)
(fact fact2 fact-acc)
> (fact 4)
|(fact 4)
| (fact 3)
| |(fact 2)
| | (fact 1)
| | |(fact 0)
| | |1
| | 1
| |2
| 6
|24
24
> (fact2 4)
|(fact2 4)
|(fact-acc 4 1)
|(fact-acc 3 4)
|(fact-acc 2 12)
|(fact-acc 1 24)
|(fact-acc 0 24)
|24
24
>