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;;;; cache.scm --- cache the results of parsing
;;;;
;;;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;;
(define-module (ice-9 peg cache)
#:export (cg-cached-parser))
;; The results of parsing using a nonterminal are cached. Think of it like a
;; hash with no conflict resolution. Process for deciding on the cache size
;; wasn't very scientific; just ran the benchmarks and stopped a little after
;; the point of diminishing returns on my box.
(define *cache-size* 512)
(define (make-cache)
(make-vector *cache-size* #f))
;; given a syntax object which is a parser function, returns syntax
;; which, if evaluated, will become a parser function that uses a cache.
(define (cg-cached-parser parser)
#`(let ((cache (make-cache)))
(lambda (str strlen at)
(let* ((vref (vector-ref cache (modulo at *cache-size*))))
;; Check to see whether the value is cached.
(if (and vref (eq? (car vref) str) (= (cadr vref) at))
(caddr vref);; If it is return it.
(let ((fres ;; Else calculate it and cache it.
(#,parser str strlen at)))
(vector-set! cache (modulo at *cache-size*)
(list str at fres))
fres))))))