From: Jim Pryor <profjim@jimpryor.net>
Date: Sun, 28 Nov 2010 01:44:03 +0000 (-0500)
Subject: ass8 blanks
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?a=commitdiff_plain;ds=sidebyside;h=826badc8d42e8fa03f46abf36273d1daadf991e7;hp=-c;p=lambda.git

ass8 blanks

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

826badc8d42e8fa03f46abf36273d1daadf991e7
diff --git a/assignment8.mdwn b/assignment8.mdwn
index c954e955..e6c6085d 100644
--- a/assignment8.mdwn
+++ b/assignment8.mdwn
@@ -60,7 +60,7 @@
 			;;
 
 
-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;
 
@@ -108,6 +108,32 @@
 		  (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)))))
@@ -127,5 +153,4 @@
 		(define tree2 '(1 . (((2 . 3) . (4 . 5)) . 6)))
 		
 		(same-fringe? tree1 tree2)
-
-
+-->