module/ice-9/hcons.scm

   1 ;;; installed-scm-file
   2
   3 ;;;;    Copyright (C) 1995, 1996, 1998, 2001, 2003, 2006 Free Software Foundation, Inc.
   4 ;;;;
   5 ;;;; This library is free software; you can redistribute it and/or
   6 ;;;; modify it under the terms of the GNU Lesser General Public
   7 ;;;; License as published by the Free Software Foundation; either
   8 ;;;; version 2.1 of the License, or (at your option) any later version.
   9 ;;;;
  10 ;;;; This library is distributed in the hope that it will be useful,
  11 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 ;;;; Lesser General Public License for more details.
  14 ;;;;
  15 ;;;; You should have received a copy of the GNU Lesser General Public
  16 ;;;; License along with this library; if not, write to the Free Software
  17 ;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  18 ;;;;
  19
  20 \f
  21 (define-module  (ice-9 hcons)
  22   :export (hashq-cons-hash hashq-cons-assoc hashq-cons-get-handle
  23            hashq-cons-create-handle! hashq-cons-ref hashq-cons-set! hashq-cons
  24            hashq-conser make-gc-buffer))
  25
  26 \f
  27 ;;; {Eq? hash-consing}
  28 ;;;
  29 ;;; A hash conser maintains a private universe of pairs s.t. if
  30 ;;; two cons calls pass eq? arguments, the pairs returned are eq?.
  31 ;;;
  32 ;;; A hash conser does not contribute life to the pairs it returns.
  33 ;;;
  34
  35 (define (hashq-cons-hash pair n)
  36   (modulo (logxor (hashq (car pair) 4194303)
  37                   (hashq (cdr pair) 4194303))
  38           n))
  39
  40 (define (hashq-cons-assoc key l)
  41   (and (not (null? l))
  42        (or (and (pair? l)               ; If not a pair, use its cdr?
  43                 (pair? (car l))
  44                 (pair? (caar l))
  45                 (eq? (car key) (caaar l))
  46                 (eq? (cdr key) (cdaar l))
  47                 (car l))
  48            (hashq-cons-assoc key (cdr l)))))
  49
  50 (define (hashq-cons-get-handle table key)
  51   (hashx-get-handle hashq-cons-hash hashq-cons-assoc table key))
  52
  53 (define (hashq-cons-create-handle! table key init)
  54   (hashx-create-handle! hashq-cons-hash hashq-cons-assoc table key init))
  55
  56 (define (hashq-cons-ref table key)
  57   (hashx-ref hashq-cons-hash hashq-cons-assoc table key #f))
  58
  59 (define (hashq-cons-set! table key val)
  60   (hashx-set! hashq-cons-hash hashq-cons-assoc table key val))
  61
  62 (define (hashq-cons table a d)
  63   (car (hashq-cons-create-handle! table (cons a d) #f)))
  64
  65 (define (hashq-conser hash-tab-or-size)
  66   (let ((table (if (vector? hash-tab-or-size)
  67                    hash-tab-or-size
  68                    (make-doubly-weak-hash-table hash-tab-or-size))))
  69     (lambda (a d) (hashq-cons table a d))))
  70
  71
  72 \f
  73
  74 (define (make-gc-buffer n)
  75   (let ((ring (make-list n #f)))
  76     (append! ring ring)
  77     (lambda (next)
  78       (set-car! ring next)
  79       (set! ring (cdr ring))
  80       next)))