assign8 tweaks

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/assignment8.mdwn b/assignment8.mdwn
index 7e358a8..abc14d0 100644 (file)
--- a/assignment8.mdwn
+++ b/assignment8.mdwn
@@ -83,8 +83,13 @@
        Some other Scheme details:
 
        *       `#t` is true and `#f` is false
        Some other Scheme details:
 
        *       `#t` is true and `#f` is false

+       *       `'(1 . 2)` and `(cons 1 2)` are pairs (the same pair)

        *       `(list)` and `'()` both evaluate to the empty list
        *       `(null? lst)` tests whether `lst` is the empty list
        *       `(list)` and `'()` both evaluate to the empty list
        *       `(null? lst)` tests whether `lst` is the empty list

+       *       non-empty lists are implemented as pairs whose second member is a list
+       *       `'() '(1) '(1 2) '(1 2 3) are all lists
+       *       `(list)` `(list1)` `(list 1 2)` `(list 1 2 3)` are the same lists
+       *       `'(1 2 3)` and `(cons 1 '(2 3))` are pairs that are also lists (the same list)

        *       `(pair? lst)` tests whether `lst` is a pair; if `lst` is a non-empty list, it will also pass this test; if `lst` fails this test, it may be because `lst` is the empty list, or because it's not a list or pair at all
        *       `(car lst)` extracts the first member of a pair / head of a list
        *       `(cdr lst)` extracts the second member of a pair / tail of a list
        *       `(pair? lst)` tests whether `lst` is a pair; if `lst` is a non-empty list, it will also pass this test; if `lst` fails this test, it may be because `lst` is the empty list, or because it's not a list or pair at all
        *       `(car lst)` extracts the first member of a pair / head of a list
        *       `(cdr lst)` extracts the second member of a pair / tail of a list


@@ -97,7 +102,6 @@
                                  (cond
                                    [(pair? tree)
                                      (helper (car tree) (lambda () (helper (cdr tree) tailk)))]
                                  (cond
                                    [(pair? tree)
                                      (helper (car tree) (lambda () (helper (cdr tree) tailk)))]

-                                   [(null? tree) (tailk)]

                                    [else (cons tree tailk)]))])
                    (helper tree (lambda () (list)))))
                
                                    [else (cons tree tailk)]))])
                    (helper tree (lambda () (list)))))
                


@@ -112,8 +116,8 @@
                (define (same-fringe? tree1 tree2)
                  (stream-equal? (lazy-flatten tree1) (lazy-flatten tree2)))
                
                (define (same-fringe? tree1 tree2)
                  (stream-equal? (lazy-flatten tree1) (lazy-flatten tree2)))
                

-               (define tree1 '(((1 2) (3 4)) (5 6)))
-               (define tree2 '(1 (((2 3) (4 5)) 6)))
+               (define tree1 '(((1 . 2) . (3 . 4)) . (5 . 6)))
+               (define tree2 '(1 . (((2 . 3) . (4 . 5)) . 6)))

                
                (same-fringe? tree1 tree2)
 
                
                (same-fringe? tree1 tree2)