;;;--------------------------------------------------------------------------
;;; 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.
+(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.
+ `:int', `:string', `:char', `:fragment', `:type'. 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.
term: factor | term `*' factor | term `/' factor
factor: primary | `+' factor | `-' factor
primary: int | id | string | `(' expression `)' | `{' fragment `}'
- | `?' lisp-expression
+ | `<' declspec+ declarator[empty] `>' | `?' lisp-expression
Only operators for dealing with integers are provided."
+
+ ;; The expression parser works in two stages. First, the parser proper
+ ;; builds a thunk as its `value'. If this is successful, then the thunk is
+ ;; invoked to return a property type and value. Primitive expressions
+ ;; produce thunks which just return their values; operators combine their
+ ;; argument thunks together, evaluating them (or not) on demand.
+
+ (macrolet ((oplambda (&body body)
+ ;; Like `lambda', but (a) always produces a function with no
+ ;; arguments, and (b) captures the current location so that
+ ;; errors are attributed correctly.
+
+ (with-gensyms (floc)
+ `(let ((,floc (file-location scanner)))
+ (lambda ()
+ (with-default-error-location (,floc)
+ ,@body))))))
+
+ (labels ((want (type thunk)
+ ;; Evaluate THUNK and convert its result to the given TYPE.
+ (multiple-value-bind (ty val) (funcall thunk)
+ (coerce-property-value val ty type)))
+
+ (int-unop (intop x)
+ ;; Evaluate X to an integer, and apply INTOP to the result,
+ ;; giving another integer.
+ (oplambda (values :int (funcall intop (want :int x)))))
+
+ (int-binop (intop x y)
+ ;; Evaluate X and Y to integers, and apply INTOP to the
+ ;; results, giving another integer.
+ (oplambda
+ (values :int (funcall intop (want :int x) (want :int y))))))
+
(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)
- (multiple-value-bind (type value)
- (decode-property sexp)
- (values (cons type value) t t))))
- (#\{
- (values (cons :fragment
- (parse-delimited-fragment scanner
- #\{ #\}))
- 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))))))))
+ (when-parse ()
+
+ ;; Parse the expression, producing a thunk.
+ (expr (:nestedp nestedp)
+
+ (lisp (case (token-type scanner)
+
+ ((:int :id :char :string)
+ ;; A simple literal.
+ (let ((type (token-type scanner))
+ (value (token-value scanner)))
+ (scanner-step scanner)
+ (values (lambda () (values type value)) t t)))
+
+ (#\?
+ ;; A Lisp s-expression. Catch and report reader-
+ ;; errors (though the main parser will probably
+ ;; end up /very/ confused); delay evaluation for
+ ;; later.
+ (handler-case
+ (let* ((stream (make-scanner-stream scanner))
+ (sexp (read stream t)))
+ (scanner-step scanner)
+ (values (oplambda (decode-property (eval sexp)))
+ t t))
+ (error (cond)
+ (scanner-step scanner)
+ (cerror*-with-location scanner
+ "Lisp `read' error: ~A"
+ cond)
+ (values #'continue t t))))
+
+ (#\{
+ ;; A code fragment.
+ (let ((fragment (parse-delimited-fragment scanner
+ #\{ #\})))
+ (values (lambda () (values :fragment fragment))
+ t t)))
+
+ (#\<
+ ;; A C type.
+ (parse (seq (#\<
+ (ds (parse-c-type scanner))
+ (dc (parse-declarator
+ scanner ds
+ :kernel (lambda ()
+ (values nil t nil))
+ :abstractp t))
+ #\>)
+ (values (lambda () (values :type (car dc)))
+ t t))))
+
+ (t
+ ;; Anything else is an error.
+ (values (list :int :id :char :string #\? #\{ #\<)
+ nil nil))))
+
+ ;; Binary operators.
+ ((:op #\* binop "*" (x y 70) (int-binop #'* x y))
+ (:op #\/ binop "/" (x y 70)
+ (oplambda
+ (let ((x (want :int x)) (y (want :int y)))
+ (when (zerop y) (error "Division by zero"))
+ (values :int (floor x y)))))
+ (:op #\+ binop "+" (x y 60) (int-binop #'+ x y))
+ (:op #\- binop "-" (x y 60) (int-binop #'- x y)))
+
+ ;; Prefix operators.
+ ((:op #\+ preop "+" (x 90) (int-unop #'identity x))
+ (:op #\- preop "-" (x 90) (int-unop #'- x))
+ (:op #\( lparen #\)))
+
+ ;; Postfix operators.
+ ((:op (when nestedp #\)) rparen #\))))
+
+ ;; Do the delayed evaluation. Establish a restart so that we can
+ ;; continue if evaluation fails for some reason. (The value thunk
+ ;; is expected to report the correct error locations, if it signals
+ ;; conditions.)
+ (restart-case (multiple-value-bind (type value) (funcall it)
+ (values (cons type value) t t))
+ (continue () (values (cons :invalid nil) t t))))))))
;;;--------------------------------------------------------------------------
;;; Parsing property sets.
+(export 'parse-property)
(defun parse-property (scanner pset)
"Parse a single property using the SCANNER; add it to the PSET."
;; property ::= id `=' expression
~mdw / sod / blobdiff