lecture code from the afternoon class.

2018-10-01-afternoon.rkt

#lang typed/racket

(require typed/rackunit)



(: my-list  (Listof Number))
(define my-list
  (cons 6 (cons 12 (cons 13+4i (cons 16 '())))))

; add the numbers in a list
(define (sum-up [l : (Listof Number)]) : Number
  (match l
    ['() 0]
    [(cons f r) (+ f (sum-up r)) ]))

(check-equal? (sum-up '()) 0)
(check-equal? (sum-up my-list)
              47+4i)