Lecture 25 :Accumulating data




Write an accumulator-style function revers that consumes a list of
strings and reverses it.


;; revers : list-of-string -> list-of-string
;; produce list of string with strings in opposite order from given list
(define (revers alos)
  (rev-accum alos empty))


;; rev-accum : list-of-string list-of-string -> list-of-string
;; accumulates reverse of first list in second list
(define (rev-accum alos revalos)
  (cond [(empty? alos) revalos]
        [(cons? alos) (rev-accum (rest alos) (cons (first alos) revalos))]))


How would we have written this in non-accumulator style?




;; reverse2 : list-of-string -> list-of-string
;; produce list of string with strings in opposite order from given list
(define (reverse2 alos)
  (cond [(empty? alos) empty]
        [(cons? alos) (append (reverse (rest alos))
                              (list (first alos)))]))



------------------------------------------------------------------