;;
-2. Here's another implementation of the same-fringe function, in Scheme. It's taken from <http://c2.com/cgi/wiki?SameFringeProblem>. It uses thunks to delay the evaluation of code that computes the tail of a list of a tree's fringe. It also involves passing continuations as arguments. Your assignment is to supply comments to the code, to explain what every significant piece is doing.
+2. Here's another implementation of the same-fringe function, in Scheme. It's taken from <http://c2.com/cgi/wiki?SameFringeProblem>. It uses thunks to delay the evaluation of code that computes the tail of a list of a tree's fringe. It also involves passing continuations as arguments. Your assignment is to fill in the blanks in the code, and also to supply comments to the code, to explain what every significant piece is doing.
This code uses Scheme's `cond` construct. That works like this;
(letrec ([helper (lambda (tree tailk)
(cond
[(pair? tree)
+ (helper (car tree) (lambda () (helper _____ tailk)))]
+ [else (cons tree tailk)]))])
+ (helper tree (lambda () _____))))
+
+ (define (stream-equal? stream1 stream2)
+ (cond
+ [(and (null? stream1) (null? stream2)) _____]
+ [(and (pair? stream1) (pair? stream2))
+ (and (equal? (car stream1) (car stream2))
+ _____)]
+ [else #f]))
+
+ (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)))
+
+ (same-fringe? tree1 tree2)
+
+
+<!--
+ (define (lazy-flatten tree)
+ (letrec ([helper (lambda (tree tailk)
+ (cond
+ [(pair? tree)
(helper (car tree) (lambda () (helper (cdr tree) tailk)))]
[else (cons tree tailk)]))])
(helper tree (lambda () (list)))))
(define tree2 '(1 . (((2 . 3) . (4 . 5)) . 6)))
(same-fringe? tree1 tree2)
-
-
+-->