Work in progress. Mostly bug fixing.

[sod] / src / pset-parse.lisp

;;; -*-lisp-*-
;;;
;;; Parsing property sets
;;;
;;; (c) 2012 Straylight/Edgeware
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This file is part of the Sensble 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.

;;;--------------------------------------------------------------------------
;;; The expression parser.

(flet ((dispatch (name args &rest spec)
	 (acond ((find :invalid args :key #'car)
		 (cons :invalid nil))
		((find-if (lambda (item)
			    (every (lambda (type arg)
				     (eql type (car arg)))
				   (cddr item)
				   args))
			  spec)
		 (cons (car it) (apply (cadr it)
				       (mapcar #'cdr args))))
		(t
		 (cerror* "Type mismatch: operator `~A' applied to ~
			       types ~{~(~A~)~#[~; and ~;, ~]~}"
			  name
			  (mapcar #'car args))
		 (cons :invalid nil)))))
  (let ((add (binop "+" (x y 5)
	       (dispatch "+" (list x y) (list :int #'+ :int :int))))
	(sub (binop "-" (x y 5)
	       (dispatch "-" (list x y) (list :int #'- :int :int))))
	(mul (binop "*" (x y 7)
	       (dispatch "*" (list x y) (list :int #'* :int :int))))
	(div (binop "/" (x y 7)
	       (dispatch "/" (list x y)
			 (list :int
			       (lambda (x y)
				 (cond ((zerop y)
					(cerror*
					 "Division by zero")
					(cons :invalid nil))
				       (t
					(floor x y))))
			       :int :int))))
	(nop (preop "+" (x 9)
	       (dispatch "+" (list x) (list :int #'+ :int))))
	(neg (preop "-" (x 9)
	       (dispatch "-" (list x) (list :int #'- :int))))
	(lp (lparen #\)))
	(rp (rparen #\))))

    (defun parse-expression (scanner)
      "Parse and evaluate a simple expression.

   The result is a pair (TYPE . VALUE).  Currently, type types are `:id',
   `:int', `:string', and `:char'.  If an error prevented a sane value from
   being produced, the type `:invalid' is returned.

   The syntax of expressions is rather limited at the moment, but more may be
   added later.

   expression: term | expression `+' term | expression `-' term
   term: factor | term `*' factor | term `/' factor
   factor: primary | `+' factor | `-' factor
   primary: int | id | string | `(' expression `)' | `?' lisp-expression

   Only operators for dealing with integers are provided."
      (with-parser-context (token-scanner-context :scanner scanner)
	(parse (expr (:nestedp nestedp)
		 (lisp (flet ((prop (type value)
				(scanner-step scanner)
				(values (cons type value) t t)))
			 (case (token-type scanner)
			   ((:int :id :char :string)
			    (prop (token-type scanner)
				  (token-value scanner)))
			   (#\?
			    (let* ((stream (make-scanner-stream scanner))
				   (sexp (read stream t)))
			      (scanner-step scanner)
			      (values (cons (property-type sexp) sexp)
				      t t)))
			   (t
			    (values (list :int :id :char :string #\?)
				    nil nil)))))
		 (or (seq (#\+) add)
		     (seq (#\-) sub)
		     (seq (#\*) mul)
		     (seq (#\/) div))
		 (or (seq (#\() lp)
		     (seq (#\+) nop)
		     (seq (#\-) neg))
		 (when nestedp (seq (#\)) rp))))))))

;;;--------------------------------------------------------------------------
;;; Parsing property sets.

(defun parse-property (scanner pset)
  "Parse a single property using the SCANNER; add it to the PSET."
  ;; property ::= id `=' expression
  (with-parser-context (token-scanner-context :scanner scanner)
    (parse (seq ((name :id) #\= (result (parse-expression scanner)))
	     (let ((type (car result))
		   (value (cdr result)))
	       (unless (eq type :invalid)
		 (add-property pset name value
			       :type type
			       :location scanner)))))))

(export 'parse-property-set)
(defun parse-property-set (scanner)
  "Parse an optional property set from the SCANNER and return it, or `nil'."
  ;; property-set ::= [`[' property-list `]']
  (with-parser-context (token-scanner-context :scanner scanner)
    (parse (? (seq (#\[
		    (pset (many (pset (make-property-set) pset)
			    (parse-property scanner pset)
			    #\,))
		    #\])
		pset)))))

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