klandergren · June 16, 2011 15:03
diff --git a/sicp2.17.scm b/sicp2.17.scm
 ;; 2.17

 ;; Helpful link on equivalence
 ;; http://sicp.ai.mit.edu/Fall-2003/manuals/scheme-7.5.5/doc/scheme_4.html

 (define (last-pair list)
  (if (null? (cdr list))
      (car list)                   ;; fixed paren error
      (last-pair (cdr list))))

 ;; testing
 (last-pair (list 1 2 3 4 5 6 4 3 23)) ;; => 23



 ;; 2.18 fails for me
 (define (reverse list)
  (if (= (cdr list) ())               ;; if statement inserted
  (= new-list (cons (car list) ())))  ;; extra paren added for if statement
     (cons (car list) (car new-list)))

 ;; Think of 2.18 in terms of 2.17: if you can find the last pair of a list
 ;; can't you call that recursively to build a new list last-element to first?

 ;; Testing
 (reverse (list 1 4 9 16 25))  ;; => (list 25 26 9 4 1)
	;; 2.17

	;; Helpful link on equivalence
	;; http://sicp.ai.mit.edu/Fall-2003/manuals/scheme-7.5.5/doc/scheme_4.html

	(define (last-pair list)
	(if (null? (cdr list))
	(car list) ;; fixed paren error
	(last-pair (cdr list))))

	;; testing
	(last-pair (list 1 2 3 4 5 6 4 3 23)) ;; => 23



	;; 2.18 fails for me
	(define (reverse list)
	(if (= (cdr list) ()) ;; if statement inserted
	(= new-list (cons (car list) ()))) ;; extra paren added for if statement
	(cons (car list) (car new-list)))

	;; Think of 2.18 in terms of 2.17: if you can find the last pair of a list
	;; can't you call that recursively to build a new list last-element to first?

	;; Testing
	(reverse (list 1 4 9 16 25)) ;; => (list 25 26 9 4 1)
No results found