1 ;; The first three lines of this file were inserted by DrScheme. They record metadata
2 ;; about the language level of this file in a form that our tools can easily process.
3 #reader(lib "htdp-intermediate-reader.ss" "lang")((modname 18.1.14-3) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp")))))
4 ;A web-page (wp) is a structure:
5 ;(make-wp header doc) where
6 ;header is a symbol and doc is
7 ;a web-document.
8 ;
9 ;A web-document (doc) is either
10 ;1. empty,
11 ;2. (cons sym doc) where sym is a symbol and
12 ;doc is a web-document, or
13 ;3. (cons wp doc) where wp is a webpage and
14 ;doc is a web-document.
15 
16 (define-struct wp (header doc))
17 
18 ;find-for-wp : wp symbol -> list-of-symbols or false. Given a-wp and a-symbol, return the headers of the web-pages that are accessed on the way to locating a-symbol within documents within a-wp. Returns false if a-symbol never occurs.  If there are 2 or more occurrences of a-symbol, find-for-wp returns a list-of-headers from only a single  occurrence by following the path that gives preference to documents before embedded web pages.
19 
20 (define (find-for-wp a-wp a-symbol) 
21   (cond 
22     [(or (cons? (find-for-doc (wp-doc a-wp) a-symbol))
23          (empty? (find-for-doc (wp-doc a-wp) a-symbol))) (cons (wp-header a-wp) (find-for-doc (wp-doc a-wp) a-symbol))]
24     [else false]))
25 
26 ;find-for-doc : doc symbol -> list-of-symbols or false
27 ;Given a-doc and a-symbol, return the headers of the web-pages that are accessed on the way to locating a-symbol within documents within a-doc (a-doc inclusive). Returns false if a-symbol never occurs. Return empty if a-doc contains a-symbol.  If there are 2 or more occurrences of a-symbol, find-for-doc returns the list-of-headers from only a single  occurrence by following the path that gives preference to documents before embedded web pages.
28 
29 (define (find-for-doc a-doc a-symbol)
30   (cond
31     [(empty? a-doc) false]
32     [else (local ((define firs )
33                   (define res ))
34             (cond    
35               [(symbol? (first a-doc))
36                (cond
37                  [(symbol=? a-symbol (first a-doc)) empty]
38                  [else (find-for-doc (rest a-doc) a-symbol)])]
39               [(or (cons? (find-for-doc (rest a-doc) a-symbol))
40                    (empty? (find-for-doc (rest a-doc) a-symbol))) (find-for-doc (rest a-doc) a-symbol)]
41               [(or (cons? (find-for-wp (first a-doc) a-symbol))
42                    (empty? (find-for-wp (first a-doc) a-symbol))) (find-for-wp (first a-doc) a-symbol)]))]))
43 
44 
45 
46 (define DOC7 (cons 'ImADoc empty))
47 (define DOC6 (cons 'ImADoc empty))
48 (define WP3 (make-wp 'ImAPage empty))
49 (define DOC5 (cons WP3 DOC6))
50 (define WP2 (make-wp 'AmIAPageToo? DOC5))
51 (define DOC4 (cons 'MaybeADoc DOC7))
52 (define DOC3 (cons WP2 DOC4))
53 (define DOC2 (cons 'ADoctor? DOC3))
54 (define DOC1 (cons 'OrADocument? DOC2))
55 (define WP1 (make-wp 'NoAWebPage DOC1))
56 
57 (find-for-wp WP1 'ImADoc)
58 
59 ;find : wp symbol -> list-of-symbols or false.
60 ;Given a-wp and a-symbol, return the headers of the web-pages that are accessed on the way to locating a-symbol within documents within a-wp. Returns false if a-symbol never occurs.  If there are 2 or more occurrences of a-symbol, find-for-wp returns a list-of-headers from only a single  occurrence by following the path that gives preference to documents before embedded web pages.
61 
62 (define (find a-wp a-symbol)
63   (local 
64     ((define (find-for-wp a-wp a-symbol)
65        (local ((define r (find-for-doc (wp-doc a-wp) a-symbol)))
66          (cond
67            [(or (cons? r)
68                 (empty? r)) (cons (wp-header a-wp) r)]
69            [else false])))
70      
71      (define (find-for-doc a-doc a-symbol)
72        (local ((define firs (find-for-wp (first a-doc) a-symbol))
73                (define res (find-for-doc (rest a-doc) a-symbol)))
74          (cond
75            [(empty? a-doc) false]
76            [(symbol? (first a-doc))
77             (cond
78               [(symbol=? a-symbol (first a-doc)) empty]
79               [else res])]
80            [(wp? (first a-doc))
81             (cond
82               [(or (cons? res)
83                    (empty? res)) res]
84               [(or (cons? firs)
85                    (empty? firs)) firs])]))))
86     (find-for-wp a-wp a-symbol)))