| ;;;; 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)))))) | |