racket-ansi/rmacs/search.rkt

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#lang racket/base
;; Knuth-Morris-Pratt string & rope search.
(provide search-generator
search-string
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search-rope
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findf-in-generator
findf-in-rope)
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(require racket/set)
(require racket/match)
(require racket/generator)
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(require "rope.rkt")
(define (table pattern)
(define t (make-vector (- (string-length pattern) 1)))
(vector-set! t 0 0)
(let loop ((pos 1) (candidate 0))
(cond
[(= pos (- (string-length pattern) 1))
t]
[(equal? (string-ref pattern pos)
(string-ref pattern candidate))
(vector-set! t pos (+ candidate 1))
(loop (+ pos 1)
(+ candidate 1))]
[(> candidate 0)
(loop pos
(vector-ref t candidate))]
[else
(vector-set! t pos 0)
(loop (+ pos 1)
0)])))
;; String (Generator Char) -> (Option Index)
(define (search-generator needle haystack)
(define t (table needle))
(define cache #f)
(define (advance!)
(define next (haystack))
(set! cache (and (char? next) next)))
(advance!)
(let loop ((m 0) (i 0))
(cond
[(not cache)
#f]
[(equal? (string-ref needle i) cache)
(if (= i (- (string-length needle) 1))
m
(begin (advance!)
(loop m (+ i 1))))]
[(> i 0)
(define ti (vector-ref t (- i 1)))
(loop (- (+ m i) ti) ti)]
[else
(advance!)
(loop (+ m 1) i)])))
;; String String -> (Option Index)
(define (search-string needle haystack)
(define t (table needle))
(let loop ((m 0) (i 0))
(cond
[(= (+ m i) (string-length haystack))
#f]
[(equal? (string-ref needle i) (string-ref haystack (+ m i)))
(if (= i (- (string-length needle) 1))
m
(loop m (+ i 1)))]
[(> i 0)
(define ti (vector-ref t (- i 1)))
(loop (- (+ m i) ti) ti)]
[else
(loop (+ m 1) i)])))
;; String Rope -> (Option Index)
(define (search-rope needle haystack #:forward? [forward? #t])
(if forward?
(search-generator needle (rope-generator haystack))
(let ((reversed-result (search-generator (list->string (reverse (string->list needle)))
(rope-generator haystack #:forward? #f))))
(and reversed-result (- (rope-size haystack) reversed-result (string-length needle))))))
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(define (findf-in-generator f gen)
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(let loop ((count 0))
(match (gen)
[(? char? c)
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(if (f c)
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count
(loop (+ count 1)))]
[_ count])))
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(define (findf-in-rope f r #:forward? [forward? #t])
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(if forward?
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(findf-in-generator f (rope-generator r))
(- (rope-size r) (findf-in-generator f (rope-generator r #:forward? #f)))))
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(module+ test
(require rackunit)
(check-equal? (table "ABCDABD")
(vector 0 0 0 0 1 2))
(check-equal? (table "PARTICIPATE IN PARACHUTE")
(vector 0 0 0 0 0 0 0 1 2 0 0 0 0 0 0 1 2 3 0 0 0 0 0))
(check-equal? (search-string "ABCDABD" "ABC ABCDAB ABCDABCDABDE") 15)
(check-equal? (search-string "AAAA" "AAABAAABAAABAAABAAAB") #f)
(check-equal? (search-generator "ABCDABD" (sequence->generator "ABC ABCDAB ABCDABCDABDE")) 15)
(check-equal? (search-generator "AAAA" (sequence->generator "AAABAAABAAABAAABAAAB")) #f)
(define prejudice-rope
(rope-concat
(map string->rope
(list "It is a truth universally acknowledged, that a single man in possession of a good fortune must be in want of a wife.\n"
"\n"
"However little known the feelings or views of such a man may be on his first entering a neighbourhood, this truth is so well fixed in the minds of the surrounding families, that he is considered as the rightful property of some one or other of their daughters.\n"
"\n"
"``My dear Mr. Bennet,'' said his lady to him one day, ``have you heard that Netherfield Park is let at last?''\n"
"\n"
"Mr. Bennet replied that he had not.\n"))))
(check-equal? (search-rope "man" prejudice-rope) 54)
(check-equal? (search-rope "man" prejudice-rope #:forward? #f) 171)
(check-equal? (search-rope "man in" prejudice-rope) 54)
(check-equal? (search-rope "man may" prejudice-rope) 171)
(check-equal? (search-rope "man may" prejudice-rope #:forward? #f) 171)
(check-equal? (search-rope "xylophone" prejudice-rope) #f)
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(check-equal? (search-rope "xylophone" prejudice-rope #:forward? #f) #f)
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(define (find-in-rope delims r)
(define chs (list->set (string->list delims)))
(findf-in-rope (lambda (c) (set-member? chs c)) r))
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(check-equal? (find-in-rope "\n" prejudice-rope) 116)
(check-equal? (find-in-rope "at" prejudice-rope) 1)
(check-equal? (find-in-rope "z" prejudice-rope) (rope-size prejudice-rope))
(check-equal? (find-in-rope "\n" prejudice-rope #:forward? #f) (rope-size prejudice-rope))
(check-equal? (find-in-rope "at" prejudice-rope #:forward? #f) (- (rope-size prejudice-rope) 2))
(check-equal? (find-in-rope "z" prejudice-rope #:forward? #f) 0))