Daniel-Nikpayuk_SICP-Solutions/Chapter 2/2.2/exercise-2.39 (fold-reverse)/exercise.lsp
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;; Copyright 2015 Daniel Nikpayuk
;;
;; This file is part of SICP Solutions.
;;
;; SICP Solutions is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License
;; as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
;;
;; SICP Solutions is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty
;; of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License along with SICP Solutions. If not, see
;; <http://www.gnu.org/licenses/>.
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(define (fold-right op initial sequence)
  (if (null? sequence)
      initial
      (op (car sequence)
          (fold-right op initial (cdr sequence)))))

(define (fold-left op initial sequence)
  (define (iter result rest)
    (if (null? rest)
        result
        (iter (op result (car rest))
              (cdr rest))))
  (iter initial sequence))

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(define (reverse sequence)
  (fold-right (lambda (x y) (append y (list x))) '() sequence))
(define (reverse sequence)
  (fold-left (lambda (x y) (cons y x)) '() sequence))

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(reverse (list 1 2 3 4))

