;; (space-added-list L) consumes a non-empty (listof Str) and return the list
;;    with a space added at the beginning of each word other than the first one
;; space-added-list : (listof Str) -> (listof Str)
;; Example :
(check-expect (space-added-list (list "Hello" "how" "are" "you?"))
              (list "Hello" " how" " are" " you?"))

(define (space-added-list L)
  (append (list (first L))
          (map (lambda (x) (string-append " " x)) (rest L))))


;; (join L) consumes a non-empty (listof Str), and returns the Str that results
;;     from appending all the values in L, with a space (" ") between them
;; join : (listof Str) -> Str
;; requires : L is a non-empty list
;; Example :
(check-expect (join (list "Hello" "how" "are" "you?")) "Hello how are you?")

(define (join L)
  (foldr string-append "" (space-added-list L)))

;; Tests :
(check-expect (join (list "I" "am" "fine" "thanks!")) "I am fine thanks!")
(check-expect (join (list "How" "is" "your" "job?")) "How is your job?")