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22d4c9d99a
* module/ice-9/peg/cache.scm: add module to hold cache logic for PEG parsers * module/ice-9/peg.scm: move cache logic out of here
45 lines
2 KiB
Scheme
45 lines
2 KiB
Scheme
;;;; cache.scm --- cache the results of parsing
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;;;;
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;;;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.
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;;;;
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;;;; This library is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU Lesser General Public
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;;;; License as published by the Free Software Foundation; either
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;;;; version 3 of the License, or (at your option) any later version.
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;;;;
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;;;; This library is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;;; Lesser General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU Lesser General Public
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;;;; License along with this library; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;;;
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(define-module (ice-9 peg cache)
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#:export (cg-cached-parser))
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;; The results of parsing using a nonterminal are cached. Think of it like a
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;; hash with no conflict resolution. Process for deciding on the cache size
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;; wasn't very scientific; just ran the benchmarks and stopped a little after
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;; the point of diminishing returns on my box.
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(define *cache-size* 512)
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(define (make-cache)
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(make-vector *cache-size* #f))
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;; given a syntax object which is a parser function, returns syntax
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;; which, if evaluated, will become a parser function that uses a cache.
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(define (cg-cached-parser parser)
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#`(let ((cache (make-cache)))
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(lambda (str strlen at)
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(let* ((vref (vector-ref cache (modulo at *cache-size*))))
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;; Check to see whether the value is cached.
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(if (and vref (eq? (car vref) str) (= (cadr vref) at))
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(caddr vref);; If it is return it.
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(let ((fres ;; Else calculate it and cache it.
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(#,parser str strlen at)))
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(vector-set! cache (modulo at *cache-size*)
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(list str at fres))
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fres))))))
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