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;;; -*- Mode: LISP; Syntax: COMMON-LISP; Package: CL-PPCRE; Base: 10 -*-
;;; $Header: /usr/local/cvsrep/cl-ppcre/parser.lisp,v 1.31 2009/09/17 19:17:31 edi Exp $
;;; The parser will - with the help of the lexer - parse a regex
;;; string and convert it into a "parse tree" (see docs for details
;;; about the syntax of these trees). Note that the lexer might
;;; return illegal parse trees. It is assumed that the conversion
;;; process later on will track them down.
;;; Copyright (c) 2002-2009, Dr. Edmund Weitz. All rights reserved.
;;; Redistribution and use in source and binary forms, with or without
;;; modification, are permitted provided that the following conditions
;;; are met:
;;; * Redistributions of source code must retain the above copyright
;;; notice, this list of conditions and the following disclaimer.
;;; * Redistributions in binary form must reproduce the above
;;; copyright notice, this list of conditions and the following
;;; disclaimer in the documentation and/or other materials
;;; provided with the distribution.
;;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR 'AS IS' AND ANY EXPRESSED
;;; OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
;;; ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
;;; DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
;;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
;;; GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
;;; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
;;; WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;; SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
(defun group (lexer)
"Parses and consumes a <group>.
The productions are: <group> -> \"\(\"<regex>\")\"
\"\(?:\"<regex>\")\"
\"\(?>\"<regex>\")\"
\"\(?<flags>:\"<regex>\")\"
\"\(?=\"<regex>\")\"
\"\(?!\"<regex>\")\"
\"\(?<=\"<regex>\")\"
\"\(?<!\"<regex>\")\"
\"\(?\(\"<num>\")\"<regex>\")\"
\"\(?\(\"<regex>\")\"<regex>\")\"
\"\(?<name>\"<regex>\")\" \(when *ALLOW-NAMED-REGISTERS* is T)
<legal-token>
where <flags> is parsed by the lexer function MAYBE-PARSE-FLAGS.
Will return <parse-tree> or \(<grouping-type> <parse-tree>) where
<grouping-type> is one of six keywords - see source for details."
(multiple-value-bind (open-token flags)
(get-token lexer)
(cond ((eq open-token :open-paren-paren)
;; special case for conditional regular expressions; note
;; that at this point we accept a couple of illegal
;; combinations which'll be sorted out later by the
;; converter
(let* ((open-paren-pos (car (lexer-last-pos lexer)))
;; check if what follows "(?(" is a number
(number (try-number lexer :no-whitespace-p t))
;; make changes to extended-mode-p local
(*extended-mode-p* *extended-mode-p*))
(cond (number
;; condition is a number (i.e. refers to a
;; back-reference)
(let* ((inner-close-token (get-token lexer))
(reg-expr (reg-expr lexer))
(close-token (get-token lexer)))
(unless (eq inner-close-token :close-paren)
(signal-syntax-error* (+ open-paren-pos 2)
"Opening paren has no matching closing paren."))
(signal-syntax-error* open-paren-pos
"Opening paren has no matching closing paren."))
(list :branch number reg-expr)))
(t
;; condition must be a full regex (actually a
;; look-behind or look-ahead); and here comes a
;; terrible kludge: instead of being cleanly
;; separated from the lexer, the parser pushes
;; back the lexer by one position, thereby
;; landing in the middle of the 'token' "(?(" -
;; yuck!!
(decf (lexer-pos lexer))
(let* ((inner-reg-expr (group lexer))
(reg-expr (reg-expr lexer))
(close-token (get-token lexer)))
(unless (eq close-token :close-paren)
(signal-syntax-error* open-paren-pos
"Opening paren has no matching closing paren."))
(list :branch inner-reg-expr reg-expr))))))
((member open-token '(:open-paren
:open-paren-colon
:open-paren-greater
:open-paren-equal
:open-paren-exclamation
:open-paren-less-equal
:open-paren-less-exclamation
:open-paren-less-letter)
:test #'eq)
;; make changes to extended-mode-p local
(let ((*extended-mode-p* *extended-mode-p*))
;; we saw one of the six token representing opening
;; parentheses
(let* ((open-paren-pos (car (lexer-last-pos lexer)))
(register-name (when (eq open-token :open-paren-less-letter)
(parse-register-name-aux lexer)))
(reg-expr (reg-expr lexer))
(close-token (get-token lexer)))
(when (or (eq open-token :open-paren)
(eq open-token :open-paren-less-letter))
;; if this is the "("<regex>")" or "(?"<name>""<regex>")" production we have to
;; increment the register counter of the lexer
(incf (lexer-reg lexer)))
(unless (eq close-token :close-paren)
;; the token following <regex> must be the closing
;; parenthesis or this is a syntax error
(signal-syntax-error* open-paren-pos
"Opening paren has no matching closing paren."))
(if flags
;; if the lexer has returned a list of flags this must
;; have been the "(?:"<regex>")" production
(cons :group (nconc flags (list reg-expr)))
(if (eq open-token :open-paren-less-letter)
(list :named-register
;; every string was reversed, so we have to
;; reverse it back to get the name
(nreverse register-name)
reg-expr)
(list (case open-token
((:open-paren)
:register)
((:open-paren-colon)
:group)
((:open-paren-greater)
:standalone)
((:open-paren-equal)
:positive-lookahead)
((:open-paren-exclamation)
:negative-lookahead)
((:open-paren-less-equal)
:positive-lookbehind)
((:open-paren-less-exclamation)
:negative-lookbehind))
reg-expr))))))
;; this is the <legal-token> production; <legal-token> is
;; any token which passes START-OF-SUBEXPR-P (otherwise
;; parsing had already stopped in the SEQ method)
open-token))))
(defun greedy-quant (lexer)
"Parses and consumes a <greedy-quant>.
The productions are: <greedy-quant> -> <group> | <group><quantifier>
where <quantifier> is parsed by the lexer function GET-QUANTIFIER.
Will return <parse-tree> or (:GREEDY-REPETITION <min> <max> <parse-tree>)."
(let* ((group (group lexer))
(token (get-quantifier lexer)))
(if token
;; if GET-QUANTIFIER returned a non-NIL value it's the
;; two-element list (<min> <max>)
(list :greedy-repetition (first token) (second token) group)
group)))
(defun quant (lexer)
"Parses and consumes a <quant>.
The productions are: <quant> -> <greedy-quant> | <greedy-quant>\"?\".
Will return the <parse-tree> returned by GREEDY-QUANT and optionally
change :GREEDY-REPETITION to :NON-GREEDY-REPETITION."
(let* ((greedy-quant (greedy-quant lexer))
(pos (lexer-pos lexer))
(next-char (next-char lexer)))
(when next-char
(if (char= next-char #\?)
(setf (car greedy-quant) :non-greedy-repetition)
(setf (lexer-pos lexer) pos)))
greedy-quant))
(defun seq (lexer)
"Parses and consumes a <seq>.
The productions are: <seq> -> <quant> | <quant><seq>.
Will return <parse-tree> or (:SEQUENCE <parse-tree> <parse-tree>)."
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(flet ((make-array-from-two-chars (char1 char2)
(let ((string (make-array 2
:element-type 'character
:fill-pointer t
:adjustable t)))
(setf (aref string 0) char1)
(setf (aref string 1) char2)
string)))
;; Note that we're calling START-OF-SUBEXPR-P before we actually try
;; to parse a <seq> or <quant> in order to catch empty regular
;; expressions
(if (start-of-subexpr-p lexer)
(let ((quant (quant lexer)))
(if (start-of-subexpr-p lexer)
(let* ((seq (seq lexer))
(quant-is-char-p (characterp quant))
(seq-is-sequence-p (and (consp seq)
(eq (first seq) :sequence))))
(cond ((and quant-is-char-p
(characterp seq))
(make-array-from-two-chars seq quant))
((and quant-is-char-p
(stringp seq))
(vector-push-extend quant seq)
seq)
((and quant-is-char-p
seq-is-sequence-p
(characterp (second seq)))
(cond ((cddr seq)
(setf (cdr seq)
(cons
(make-array-from-two-chars (second seq)
quant)
(cddr seq)))
seq)
(t (make-array-from-two-chars (second seq) quant))))
((and quant-is-char-p
seq-is-sequence-p
(stringp (second seq)))
(cond ((cddr seq)
(setf (cdr seq)
(cons
(progn
(vector-push-extend quant (second seq))
(second seq))
(cddr seq)))
seq)
(t
(vector-push-extend quant (second seq))
(second seq))))
(seq-is-sequence-p
;; if <seq> is also a :SEQUENCE parse tree we merge
;; both lists into one to avoid unnecessary consing
(setf (cdr seq)
(cons quant (cdr seq)))
seq)
(t (list :sequence quant seq))))
quant))
:void)))
(defun reg-expr (lexer)
"Parses and consumes a <regex>, a complete regular expression.
The productions are: <regex> -> <seq> | <seq>\"|\"<regex>.
Will return <parse-tree> or (:ALTERNATION <parse-tree> <parse-tree>)."
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(let ((pos (lexer-pos lexer)))
(case (next-char lexer)
((nil)
;; if we didn't get any token we return :VOID which stands for
;; "empty regular expression"
:void)
((#\|)
;; now check whether the expression started with a vertical
;; bar, i.e. <seq> - the left alternation - is empty
(list :alternation :void (reg-expr lexer)))
(otherwise
;; otherwise un-read the character we just saw and parse a
;; <seq> plus the character following it
(setf (lexer-pos lexer) pos)
(let* ((seq (seq lexer))
(pos (lexer-pos lexer)))
(case (next-char lexer)
((nil)
;; no further character, just a <seq>
seq)
((#\|)
;; if the character was a vertical bar, this is an
;; alternation and we have the second production
(let ((reg-expr (reg-expr lexer)))
(cond ((and (consp reg-expr)
(eq (first reg-expr) :alternation))
;; again we try to merge as above in SEQ
(setf (cdr reg-expr)
(cons seq (cdr reg-expr)))
reg-expr)
(t (list :alternation seq reg-expr)))))
(otherwise
;; a character which is not a vertical bar - this is
;; either a syntax error or we're inside of a group and
;; the next character is a closing parenthesis; so we
;; just un-read the character and let another function
;; take care of it
(setf (lexer-pos lexer) pos)
seq)))))))
(defun reverse-strings (parse-tree)
"Recursively walks through PARSE-TREE and destructively reverses all
strings in it."
(declare #.*standard-optimize-settings*)
(cond ((stringp parse-tree)
(nreverse parse-tree))
((consp parse-tree)
(loop for parse-tree-rest on parse-tree
while parse-tree-rest
do (setf (car parse-tree-rest)
(reverse-strings (car parse-tree-rest))))
parse-tree)
(t parse-tree)))
(defun parse-string (string)
"Translate the regex string STRING into a parse tree."
(let* ((lexer (make-lexer string))
(parse-tree (reverse-strings (reg-expr lexer))))
;; check whether we've consumed the whole regex string
(if (end-of-string-p lexer)
parse-tree
(signal-syntax-error* (lexer-pos lexer) "Expected end of string."))))