(define letter-to-number
  (lambda (letter)
    (if (eq? letter 'A)
	4.0
	(if (eq? letter 'B+)
	    3.5
	    3.0))))

(letter-to-number 'A)
(letter-to-number 'B+)
(letter-to-number 'B)

(define letter-to-number
  (lambda (letter)
    (cond
     [(eq? letter 'A) 4.0]
     [(eq? letter 'B+) 3.5]
     [else 3.0])))

(define letter-to-number
  (lambda (letter)
    (case letter
      [(A) 4.0]
      [(B+) 3.5]
      [else 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 '())
(largest-in-list '(3 5 2 4))
(largest-in-list '(-3 -1))

(define make-adder
  (lambda (m)
    (lambda (n)
      (+ n m))))
make-adder
(define add5 (make-adder 5))
add5
(add5 6)
((make-adder 5) 6)
(((lambda (m)
    (lambda (n)
      (+ n m)))
  5)
 6)
(define f (lambda (a b) (+ (* 2 a) b)))
(f 6 7)
(define a 12)
(let ([a 7] [b (+ a 2)])
  (+ a b))
a