71 lines
2.8 KiB
Scheme
71 lines
2.8 KiB
Scheme
;;; b-tree.scm - a B-tree for Xanadu
|
|
;;;
|
|
;;; Copyright (c) 2011-2012 Johan Ceuppens
|
|
;;;
|
|
;;; All rights reserved.
|
|
;;;
|
|
;;; Redistribution and use in source and binary forms, with or without
|
|
;;; modification, are permitted provided that the following conditions
|
|
;;; are met:
|
|
;;; 1. Redistributions of source code must retain the above copyright
|
|
;;; notice, this list of conditions and the following disclaimer.
|
|
;;; 2. Redistributions in binary form must reproduce the above copyright
|
|
;;; notice, this list of conditions and the following disclaimer in the
|
|
;;; documentation and/or other materials provided with the distribution.
|
|
;;; 3. The name of the authors may not be used to endorse or promote products
|
|
;;; derived from this software without specific prior written permission.
|
|
;;;
|
|
;;; THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
|
|
;;; IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
|
|
;;; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
|
|
;;; IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
;;; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
|
|
;;; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
|
|
;;; DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
|
|
;;; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
|
|
;;; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
|
|
;;; THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
|
|
|
(define (vector-median v)
|
|
(let ((len (ceiling (/ (vector-length v) 2))))
|
|
(let ((retl (make-vector len))
|
|
(retr (make-vector len)))
|
|
(do ((i 0 (+ i 1)))
|
|
((= i len) (list retl retr))
|
|
(vector-set! retl i (vector-ref v i))
|
|
(vector-set! retr (- len (- i 1)) (vector-ref v (- len (- i 1))))
|
|
))))
|
|
|
|
(define (make-b-tree)
|
|
(let ((*tree (make-vector 0)))
|
|
|
|
(define (goto-left-node str i tree)
|
|
(cond ((= (vector-length tree) i) (display "null node") (vector-set! tree i str))
|
|
(else #f)))
|
|
|
|
(define (grow-up upper-node)
|
|
(cond ((eq? node *tree)
|
|
(set! *tree (vector-median *tree
|
|
|
|
(define (add-rec str tree upper-node)
|
|
(do ((i 0 (+ i 1)))
|
|
((eq? i (vector-length tree))
|
|
(grow-up upper-node)
|
|
(let ((vi (vector-ref tree i)))
|
|
(cond ((string<=? str vi)
|
|
0)
|
|
((string>=? str vi)
|
|
(grow-down))
|
|
((string=? str vi)
|
|
(set! i (vector-length tree)))
|
|
(else (display "never reached."))))
|
|
))
|
|
|
|
(define (add str)
|
|
(add-rec *tree *tree))
|
|
|
|
(define (dispatch msg)
|
|
(cond ((eq? msg 'add) add)
|
|
(else (display "b-tree : message not understood."))))
|
|
dispatch))
|