src/lexer-{proto,impl}.lisp: Add explicit recovery action to `error'.

[sod] / src / lexer-impl.lisp

;;; -*-lisp-*-
;;;
;;; Implementation of lexical analysis protocol.
;;;
;;; (c) 2009 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This file is part of the Sensible Object Design, an object system for C.
;;;
;;; SOD is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 2 of the License, or
;;; (at your option) any later version.
;;;
;;; SOD 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 General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with SOD; if not, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

(cl:in-package #:sod)

;;;--------------------------------------------------------------------------
;;; Class implementation.

(defmethod shared-initialize :after
    ((scanner sod-token-scanner) slot-names &key)
  (default-slot (scanner 'sod-parser::filename slot-names)
    (scanner-filename (token-scanner-char-scanner scanner))))

(defmethod make-scanner-stream ((scanner sod-token-scanner))
  (make-scanner-stream (token-scanner-char-scanner scanner)))

;;;--------------------------------------------------------------------------
;;; Indicators and error messages.

(defun show-char (char)
  "Format CHAR as a string in a readable way."
  (cond ((null char) "<end-of-file>")
	((and (graphic-char-p char) (char/= char #\space))
	 (format nil "`~C'" char))
	(t (format nil "<~(~:C~)>" char))))

(defun %skip-until (scanner token-types
		    &key (keep-end (not (null (cdr token-types)))))
  "This is the implementation of the `skip-until' parser."
  (do ((consumedp nil t))
      ((let ((type (token-type scanner))
	     (value (token-value scanner)))
	 (some (lambda (spec)
		 (multiple-value-bind (want-type want-value)
		     (cond ((listp spec) (values (car spec) (cadr spec)))
			   (t (values spec t)))
		   (and (eq want-type type)
			(or (eq want-value t)
			    (equal want-value value)))))
	       token-types))
       (unless keep-end (scanner-step scanner))
       (values nil t (or keep-end consumedp)))
    (when (scanner-at-eof-p scanner)
      (return (values token-types nil consumedp)))
    (scanner-step scanner)))

(defun parse-error-recover (scanner parser recover
			    &key ignore-unconsumed force-progress action)
  "This is the implementation of the `error' parser."
  (multiple-value-bind (result win consumedp) (funcall parser)
    (cond ((or win
	       (and (not consumedp)
		    (or ignore-unconsumed
			(scanner-at-eof-p scanner))))
	   ;; If we succeeded, or if we didn't consume any tokens and the
	   ;; caller's OK with that, then there's nothing for us to do here.
	   ;; On the other hand, if we failed, didn't consume any tokens, and
	   ;; we're at end-of-file, then there's not much hope of making
	   ;; onward progress, so in this case we propagate the failure
	   ;; rather than trying to recover.  And we assume that the
	   ;; continuation will somehow arrange to report the problem, and
	   ;; avoid inundating the user with error reports.
	   (values result win consumedp))
	  (t
	   ;; Now we have to do some kind of sensible error recovery.  The
	   ;; important thing to do here is to make sure that we make some
	   ;; progress.  If we consumed any tokens then we're fine, and we'll
	   ;; just try the provided recovery strategy.  Otherwise, if we're
	   ;; not at EOF, then we can ensure progress by discarding the
	   ;; current token.  Finally, if we are at EOF then our best bet is
	   ;; simply to propagate the current failure back to the caller, but
	   ;; we handled that case above.
	   (syntax-error scanner result)
	   (when action (funcall action))
	   (when (and force-progress (not consumedp)) (scanner-step scanner))
	   (funcall recover)))))

;;;--------------------------------------------------------------------------
;;; Token scanning.

(defmethod scanner-token ((scanner sod-token-scanner))
  (with-slots (char-scanner line column) scanner
    (with-parser-context (character-scanner-context :scanner char-scanner)

      (flet ((scan-digits (&key (radix 10) (min 1) (init 0))
	       ;; Scan and return a sequence of digits.
	       (parse (many (acc init (+ (* acc radix) it) :min min)
			(label (list :digit radix)
			       (filter (lambda (ch)
					 (digit-char-p ch radix)))))))
	     (start-floc ()
	       ;; This is a little nasty.  We scan the first token during
	       ;; instance initialization, as a result of `shared-initialize'
	       ;; on `token-scanner'.  Unfortunately, this happens before
	       ;; we've had a chance to initialize our own `filename' slot.
	       ;; This means that we can't use the SCANNER as a file
	       ;; location, however tempting it might be.  So we have this
	       ;; hack.
	       (make-file-location (scanner-filename char-scanner)
				   (scanner-line scanner)
				   (scanner-column scanner))))

	;; Skip initial junk, and remember the place.
	(loop
	  (setf (scanner-line scanner) (scanner-line char-scanner)
		(scanner-column scanner) (scanner-column char-scanner))
	  (cond-parse (:consumedp cp :expected exp)
	    ((satisfies whitespace-char-p) (parse :whitespace))
	    ((scan-comment char-scanner))
	    (t (if cp (lexer-error char-scanner exp) (return)))))

	;; Now parse something.
	(cond-parse (:consumedp cp :expected exp)

	  ;; Alphanumerics mean we read an identifier.
	  ((or #\_ (satisfies alpha-char-p))
	   (values :id (with-output-to-string (out)
			 (write-char it out)
			 (parse (many (nil nil (write-char it out))
				  (or #\_ (satisfies alphanumericp)))))))

	  ;; Quotes introduce a literal.
	  ((seq ((quote (or #\" #\'))
		 (contents (many (out (make-string-output-stream)
				      (progn (write-char it out) out)
				      :final (get-output-stream-string out))
			     (or (and #\\ :any) (not quote))))
		 (nil (or (char quote)
			  (seq (:eof)
			    (lexer-error char-scanner (list quote))
			    (info-with-location
			     (start-floc) "Literal started here")))))
	     (ecase quote
	       (#\" contents)
	       (#\' (case (length contents)
		      (1 (char contents 0))
		      (0 (cerror*-with-location (start-floc)
						'simple-lexer-error
						:format-control
						"Empty character literal")
			 #\?)
		      (t (cerror*-with-location (start-floc)
						'simple-lexer-error
						:format-control
						"Too many characters ~
						 in character literal")
			 (char contents 0))))))
	   (values (etypecase it
		     (character :char)
		     (string :string))
		   it))

	  ;; Zero introduces a chosen-radix integer.
	  ((and #\0
		(or (and (or #\b #\B) (scan-digits :radix 2))
		    (and (or #\o #\O) (scan-digits :radix 8))
		    (and (or #\x #\X) (scan-digits :radix 16))
		    (scan-digits :radix 8 :min 0)))
	   (values :int it))

	  ;; Any other digit forces radix-10.
	  ((seq ((d (filter digit-char-p))
		 (i (scan-digits :radix 10 :min 0 :init d)))
	     i)
	   (values :int it))

	  ;; Some special punctuation sequences are single tokens.
	  ("..." (values :ellipsis nil))

	  ;; Any other character is punctuation.
	  (:any (values it nil))

	  ;; End of file means precisely that.
	  (:eof (values :eof nil))

	  ;; Report errors and try again.  Because we must have consumed some
	  ;; input in order to get here (we've matched both :any and :eof) we
	  ;; must make progress on every call.
	  (t
	   (assert cp)
	   (lexer-error char-scanner exp)
	   (scanner-token scanner)))))))

;;;----- That's all, folks --------------------------------------------------