ice-9/hcons.scm

   1 ;;; installed-scm-file
   2
   3 ;;;;    Copyright (C) 1995, 1996, 1998 Free Software Foundation, Inc.
   4 ;;;;
   5 ;;;; This program is free software; you can redistribute it and/or modify
   6 ;;;; it under the terms of the GNU General Public License as published by
   7 ;;;; the Free Software Foundation; either version 2, or (at your option)
   8 ;;;; any later version.
   9 ;;;;
  10 ;;;; This program 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
  13 ;;;; GNU General Public License for more details.
  14 ;;;;
  15 ;;;; You should have received a copy of the GNU General Public License
  16 ;;;; along with this software; see the file COPYING.  If not, write to
  17 ;;;; the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18 ;;;; Boston, MA 02111-1307 USA
  19 ;;;;
  20
  21 \f
  22 (define-module  (ice-9 hcons))
  23
  24 \f
  25 ;;; {Eq? hash-consing}
  26 ;;;
  27 ;;; A hash conser maintains a private universe of pairs s.t. if
  28 ;;; two cons calls pass eq? arguments, the pairs returned are eq?.
  29 ;;;
  30 ;;; A hash conser does not contribute life to the pairs it returns.
  31 ;;;
  32
  33 (define-public (hashq-cons-hash pair n)
  34   (modulo (logxor (hashq (car pair) 4194303)
  35                   (hashq (cdr pair) 4194303))
  36           n))
  37
  38 (define-public (hashq-cons-assoc key l)
  39   (and (not (null? l))
  40        (or (and (pair? l)               ; If not a pair, use its cdr?
  41                 (pair? (car l))
  42                 (pair? (caar l))
  43                 (eq? (car key) (caaar l))
  44                 (eq? (cdr key) (cdaar l))
  45                 (car l))
  46            (hashq-cons-assoc key (cdr l)))))
  47
  48 (define-public (hashq-cons-get-handle table key)
  49   (hashx-get-handle hashq-cons-hash hashq-cons-assoc table key #f))
  50
  51 (define-public (hashq-cons-create-handle! table key init)
  52   (hashx-create-handle! hashq-cons-hash hashq-cons-assoc table key init))
  53
  54 (define-public (hashq-cons-ref table key)
  55   (hashx-ref hashq-cons-hash hashq-cons-assoc table key #f))
  56
  57 (define-public (hashq-cons-set! table key val)
  58   (hashx-set! hashq-cons-hash hashq-cons-assoc table key val))
  59
  60 (define-public (hashq-cons table a d)
  61   (car (hashq-cons-create-handle! table (cons a d) #f)))
  62
  63 (define-public (hashq-conser hash-tab-or-size)
  64   (let ((table (if (vector? hash-tab-or-size)
  65                    hash-tab-or-size
  66                    (make-doubly-weak-hash-table hash-tab-or-size))))
  67     (lambda (a d) (hashq-cons table a d))))
  68
  69
  70 \f
  71
  72 (define-public (make-gc-buffer n)
  73   (let ((ring (make-list n #f)))
  74     (append! ring ring)
  75     (lambda (next)
  76       (set-car! ring next)
  77       (set! ring (cdr ring))
  78       next)))