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Diffstat (limited to 'third_party/lisp/npg/src/parser.lisp')
| -rw-r--r-- | third_party/lisp/npg/src/parser.lisp | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/third_party/lisp/npg/src/parser.lisp b/third_party/lisp/npg/src/parser.lisp new file mode 100644 index 0000000000..328be1dcf3 --- /dev/null +++ b/third_party/lisp/npg/src/parser.lisp @@ -0,0 +1,234 @@ +;;; parser.lisp --- runtime parser + +;;; Copyright (C) 2003-2006, 2009 by Walter C. Pelissero + +;;; Author: Walter C. Pelissero <walter@pelissero.de> +;;; Project: NPG a Naive Parser Generator + +#+cmu (ext:file-comment "$Module: parser.lisp $") + +;;; 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 2.1 +;;; 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., 59 Temple Place, Suite 330, Boston, MA +;;; 02111-1307 USA + +;;; Commentary: +;;; +;;; This is the runtime part of the parser. The code that is +;;; responsible to execute the parser defined with the primitives +;;; found in define.lisp. + +(in-package :naive-parser-generator) + +(defvar *debug* nil + "Either nil or a stream where to write the debug informations.") +#+debug (declaim (fixnum *maximum-recursion-depth*)) +#+debug (defvar *maximum-recursion-depth* 1000 + "Maximum depth the parser is allowed to recursively call itself. +This is the only way for the parser to detect a loop in the grammar. +Tune this if your grammar is unusually complex.") + +(declaim (inline reduce-production)) +(defun reduce-production (production arguments) + "Apply PRODUCTION's action on ARGUMENTS. This has the effect of + \"reducing\" the production." + (when *debug* + (format *debug* "reducing ~S on ~S~%" production arguments)) + (flet ((safe-token-value (token) + (if (token-p token) + (token-value token) + token))) + (apply (prod-action production) (mapcar #'safe-token-value arguments)))) + +(defgeneric later-position (pos1 pos2) + (:documentation + "Compare two file postions and return true if POS1 is later than +POS2 in the input stream.")) + +;; This is meant to be overloaded in the lexer +(defmethod later-position ((pos1 integer) (pos2 integer)) + (> pos1 pos2)) + +;; this looks silly but turns out to be useful (see below) +(defmethod later-position (pos1 pos2) + (and (eq pos1 :eof) (not (eq pos2 :eof)))) + +(defgeneric read-next-tokens (tokens-source) + (:documentation "Read next token from a lexical analysed stream. The nature of +TOKENS-SOURCE is implementation dependent and any lexical analyzer is +supposed to specialise this method.")) + +;; This is the actual parser. the algorithm is pretty +;; straightforward, the execution of the reductions a bit less. Error +;; recovery is rather clumsy. + +(defun parse (grammar start tokenizer) + "Match a GRAMMAR against the list of input tokens coming from TOKENIZER. +Return the reduced values according to the nonterminal actions. Raise +an error on failure." + (declare (type grammar grammar) + (type symbol start)) + (labels + ((match-token (expected token) + (when *debug* + (format *debug* "match-token ~S ~S -> " expected token)) + (let ((res (cond ((symbolp expected) + ;; non-costant terminal (like identifiers) + (eq expected (token-type token))) + ((and (stringp expected) + (stringp (token-value token))) + ;; string costant terminal + (funcall (the function (grammar-equal-p grammar)) expected (token-value token))) + ((functionp expected) + ;; custom equality predicate (must be able + ;; to deal with token objects) + (funcall expected token)) + ;; all the rest + (t (equal expected (token-value token)))))) + (when *debug* + (format *debug* "~Amatched~%" (if res "" "not "))) + res)) + (match (expected matched #+debug depth) + (declare (list expected matched) + #+debug (fixnum depth)) + (let ((first-expected (car expected))) + (cond #+debug ((> depth *maximum-recursion-depth*) + (error "endless recursion on ~A ~A at ~A expecting ~S" + (token-type (car matched)) (token-value (car matched)) + (token-position (car matched)) expected)) + ((eq first-expected :any) + (match (cdr expected) (cdr matched) #+debug depth)) + ;; This is a trick to obtain partial parses. When we + ;; reach this expected token we assume we succeeded + ;; the parsing and return the remaining tokens as + ;; part of the match. + ((eq first-expected :rest) + ;; we could be at the end of input so we check this + (unless (cdr matched) + (setf (cdr matched) (list :rest))) + (list nil nil)) + ((rule-p first-expected) + ;; If it's a rule, then we try to match all its + ;; productions. We return the first that succeeds. + (loop + for production in (rule-productions first-expected) + for production-tokens of-type list = (prod-tokens production) + with last-error-position = nil + with last-error = nil + for (error-position error-descr) = + (progn + (when *debug* + (format *debug* "trying to match ~A: ~S~%" + (rule-name first-expected) production-tokens)) + (match (append production-tokens (cdr expected)) matched #+debug (1+ depth))) + do (cond ((not error-position) + (return (let ((args-count (prod-tokens-length production))) + (setf (cdr matched) + (cons (reduce-production + production + (subseq (the list (cdr matched)) 0 args-count)) + (nthcdr (1+ args-count) matched))) + (list nil nil)))) + ((or (not last-error) + (later-position error-position last-error-position)) + (setf last-error-position error-position + last-error error-descr))) + ;; if everything fails return the "best" error + finally (return (list last-error-position + (if *debug* + #'(lambda () + (format nil "~A, trying to match ~A" + (funcall (the function last-error)) + (rule-name first-expected))) + last-error))))) + (t + ;; if necessary load the next tokens + (when (null (cdr matched)) + (setf (cdr matched) (read-next-tokens tokenizer))) + (cond ((and (or (null expected) (eq first-expected :eof)) + (null (cdr matched))) + ;; This point is reached only once for each complete + ;; parsing. The expected tokens and the input + ;; tokens have been exhausted at the same time. + ;; Hence we succeeded the parsing. + (setf (cdr matched) (list :eof)) + (list nil nil)) + ((null expected) + ;; Garbage at end of parsing. This may mean that we + ;; have considered a production completed too soon. + (list (token-position (car matched)) + #'(lambda () + "garbage at end of parsing"))) + ((null (cdr matched)) + ;; EOF error + (list :eof + #'(lambda () + (format nil "end of input expecting ~S" expected)))) + (t ;; normal token + (let ((first-token (cadr matched))) + (if (match-token first-expected first-token) + (match (cdr expected) (cdr matched) #+debug depth) + ;; failed: we return the error + (list (token-position first-token) + #'(lambda () + (format nil "expected ~S but got ~S ~S" + first-expected (token-type first-token) + (token-value first-token))))))))))))) + (declare (inline match-token)) + (let ((result (list :head))) + (destructuring-bind (error-position error) + (match (list (find-rule start (grammar-rules grammar))) result #+debug 0) + (when error-position + (error "~A at ~A~%" (funcall (the function error)) error-position)) + (cadr result))))) + +(defgeneric terminals-in-grammar (grammar-or-hashtable) + (:documentation + "Find non constant terminal symbols in GRAMMAR.")) + +(defmethod terminals-in-grammar ((grammar hash-table)) + (loop + for rule being each hash-value of grammar + with terminals = '() + do (loop + for prod in (rule-productions rule) + do (loop + for tok in (prod-tokens prod) + when (symbolp tok) + do (pushnew tok terminals))) + finally (return terminals))) + +(defmethod terminals-in-grammar ((grammar grammar)) + (terminals-in-grammar (grammar-rules grammar))) + +(defun print-grammar-figures (grammar &optional (stream *standard-output*)) + (format stream "rules: ~A~%constant terminals: ~A~%variable terminals: ~S~%" + (hash-table-count (grammar-rules grammar)) + (hash-table-count (grammar-keywords grammar)) + (terminals-in-grammar (grammar-rules grammar)))) + + +(defun grammar-keyword-p (keyword grammar) + "Check if KEYWORD is part of this grammar." + (find-keyword keyword (grammar-keywords grammar))) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(defvar *grammars* (make-hash-table)) + +(defun find-grammar (name) + (gethash name *grammars*)) + +(defun delete-grammar (name) + (remhash name *grammars*)) + +(defun add-grammar (name grammar) + (setf (gethash name *grammars*) grammar)) |