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

> (define letter-to-number
  (lambda (letter)
    (if (eq? letter 'A)
	4.0
	(if (eq? letter 'B+)
	    3.5
	    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)
    (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])))
> (letter-to-number 'A)
4.0
> (letter-to-number 'B+)
3.5
> (letter-to-number 'B)
3
> (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-so-far rest-of-list)
    (if (null? rest-of-list)
	largest-so-far
	(largest-in-nonempty
	 (max largest-so-far (car rest-of-list))
	 (cdr rest-of-list)))))
> (largest-in-list '())
Exception in largest-in-list: empty list
> (define make-adder
  (lambda (n)
    (lambda (m)
      (+ n m))))
> (make-adder 5)
#<procedure>
> (define add5 (make-adder 5))
> (add5 6)
11
> ((make-adder 5) 6)
11
> (((lambda (n)
    (lambda (m)
      (+ n m)))
  5)
6)
11
>