Daniel-Nikpayuk_SICP-Solutions/Chapter 3/3.1/exercise-3.08/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 (make-f a)
 (lambda (x) (let ((b a)) (set! a x) b)); return a, set a to x.
)

(define f (make-f 0))

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;(+ (f 0) (f 1)):

;eval left:
;(+ 0 0)
;0

;eval right:
;(+ 1 0)
;1

