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

> (define letter-to-number
  (lambda (letter)
    (cond
     [(eq? letter 'A) 4.0]
     [(eq? letter 'B+) 3.5]
     [else 3.0])))
> (letter-to-number 'A)
4.0
> (letter-to-number 'B+)
3.5
> (letter-to-number 'B)
3.0
> (define letter-to-number
  (lambda (letter)
    (case letter
      [(A) 4.0]
      [(B+) 3.5]
      [else 3.0])))
> (letter-to-number 'A)
4.0
> (letter-to-number 'B+)
3.5
> (letter-to-number 'B)
3.0
> (define largest-in-list
  (lambda (lon)
    (if (null? lon)
	(errorf 'largest-in-list "empty list")
	(largest-in-nonempty (car lon) (cdr lon)))))
> 
(define largest-in-nonempty
  (lambda (largest-seen unseen)
    (if (null? unseen)
	largest-seen
	(largest-in-nonempty (max largest-seen (car unseen))
			     (cdr unseen)))))
> 
(largest-in-list '())
Exception in largest-in-list: empty list
> (define make-adder
  (lambda (m)
    (lambda (n)
      (+ n m))))
> make-adder
#<procedure>
> (define add5 (make-adder 5))
> add5
#<procedure>
> (add5 6)
11
> ((make-adder 5) 6)
11
> (((lambda (m)
    (lambda (n)
      (+ n m)))
  5)
 6)
11
> (define f (lambda (a b) (+ (* 2 a) b)))
> (f 6 7)
19
> (let ([a 7] [b 6])
  (+ a b))
13
> (let ([a 7] [b (+ a 2)])
  (+ a b))
Exception: variable a is not bound
> (let* ([a 7] [b (+ a 2)])
  (+ a b))
16
> (define a 12)
> (let ([a 7] [b (+ a 2)])
  (+ a b))
21
> a
12
>