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;;;; using-parsers.scm --- utilities to make using parsers easier
;;;;
;;;; 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 using-parsers)
#:use-module (ice-9 peg simplify-tree)
#:use-module (ice-9 peg codegen)
#:use-module (ice-9 peg cache)
#:use-module (srfi srfi-9)
#:export (match-pattern define-peg-pattern search-for-pattern
prec make-prec peg:start peg:end peg:string
peg:tree peg:substring peg-record?))
(define-record-type prec
(make-prec start end string tree)
peg-record?
(start prec-start)
(end prec-end)
(string prec-string)
(tree prec-tree))
(define (peg:start pm)
(and pm (prec-start pm)))
(define (peg:end pm)
(and pm (prec-end pm)))
(define (peg:string pm)
(and pm (prec-string pm)))
(define (peg:tree pm)
(and pm (prec-tree pm)))
(define (peg:substring pm)
(and pm (substring (prec-string pm) (prec-start pm) (prec-end pm))))
;;;
;;; Helper Macros
;;;
(define-syntax until
(syntax-rules ()
"Evaluate TEST. If it is true, return its value. Otherwise,
execute the STMTs and try again."
((_ test stmt stmt* ...)
(let lp ()
(or test
(begin stmt stmt* ... (lp)))))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;; FOR DEFINING AND USING NONTERMINALS
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Parses STRING using NONTERM
(define (match-pattern nonterm string)
;; We copy the string before using it because it might have been modified
;; in-place since the last time it was parsed, which would invalidate the
;; cache. Guile uses copy-on-write for strings, so this is fast.
(let ((res (nonterm (string-copy string) (string-length string) 0)))
(if (not res)
#f
(make-prec 0 (car res) string (string-collapse (cadr res))))))
;; Defines a new nonterminal symbol accumulating with ACCUM.
(define-syntax define-peg-pattern
(lambda (x)
(syntax-case x ()
((_ sym accum pat)
(let ((matchf (compile-peg-pattern #'pat (syntax->datum #'accum)))
(accumsym (syntax->datum #'accum)))
;; CODE is the code to parse the string if the result isn't cached.
(let ((syn (wrap-parser-for-users x matchf accumsym #'sym)))
#`(define sym #,(cg-cached-parser syn))))))))
(define (peg-like->peg pat)
(syntax-case pat ()
(str (string? (syntax->datum #'str)) #'(peg str))
(else pat)))
;; Searches through STRING for something that parses to PEG-MATCHER. Think
;; regexp search.
(define-syntax search-for-pattern
(lambda (x)
(syntax-case x ()
((_ pattern string-uncopied)
(let ((pmsym (syntax->datum #'pattern)))
(let ((matcher (compile-peg-pattern (peg-like->peg #'pattern) 'body)))
;; We copy the string before using it because it might have been
;; modified in-place since the last time it was parsed, which would
;; invalidate the cache. Guile uses copy-on-write for strings, so
;; this is fast.
#`(let ((string (string-copy string-uncopied))
(strlen (string-length string-uncopied))
(at 0))
(let ((ret (until (or (>= at strlen)
(#,matcher string strlen at))
(set! at (+ at 1)))))
(if (eq? ret #t) ;; (>= at strlen) succeeded
#f
(let ((end (car ret))
(match (cadr ret)))
(make-prec
at end string
(string-collapse match))))))))))))
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