Accompany mex.pdf

sum.rkt

#lang racket

;; Non-tail
(define sum1
  (λ (n)
    (if (= n 0) n
        (+ n (sum1 (- n 1))))))

(sum1 10)

;; Tail call
(define sum2
  (λ (n)
    (letrec [(suma (λ (n acc)
                       (if (= n 0) acc
                           (suma (- n 1) (+ acc n)))))]
      (suma n 0))))

(sum2 10)

;; Theorem
(define sum3
  (λ (n)
    (/ (+ n (* n n)) 2)))

(sum3 10)