1-9-1.rkt~

;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname 1-9-1) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
; A List-of-amounts is one of: 
; – '()
; – (cons PositiveNumber List-of-amounts)

; List-of-amounts -> Number
; computes the sum of all amounts in the list
(define (sum l)
  (cond [(empty? l) 0]
        [else (+ (sum (rest l)) (first l))]))