;;;--------------------------------------------------------------------------
;;; 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', `:char', `:fragment', `:type'. 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.
| `<' 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))))))
+
+ (flet ((dispatch (name args &rest spec)
+ (oplambda
+ (let ((args (mapcar (compose #'funcall #'cons) args)))
+ (aif (find-if (lambda (item)
+ (every (lambda (type arg)
+ (eql type (car arg)))
+ (cddr item) args))
+ spec)
+ (values (car it) (apply (cadr it) (mapcar #'cdr args)))
+ (error "Type mismatch: operator `~A' applied to ~
+ types ~{~(~A~)~#[~; and ~;, ~]~}"
+ name (mapcar #'car args)))))))
+
(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)
- (restart-case (decode-property (eval sexp))
- (continue () (values :invalid nil)))
- (values (cons type value) t t))))
- (#\{
- (values (cons :fragment
- (parse-delimited-fragment scanner
- #\{ #\}))
- t t))
- (#\<
- (parse (seq (#\<
- (ds (parse-c-type scanner))
- (dc (parse-declarator
- scanner ds
- :kernel (lambda ()
- (values nil t nil))
- :abstractp t))
- #\>)
- (values (cons :type (car dc))
- 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)
+ (let ((type (token-type scanner))
+ (value (token-value scanner)))
+ (scanner-step scanner)
+ (values (lambda () (values type value)) t t)))
+ (#\?
+ (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))))
+ (#\{
+ (let ((fragment (parse-delimited-fragment scanner
+ #\{ #\})))
+ (values (lambda () (values :fragment fragment))
+ t t)))
+ (#\<
+ (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
+ (values (list :int :id :char :string #\? #\{ #\<)
+ nil nil))))
+
+ ((:op #\* binop "*" (x y 7)
+ (dispatch "*" (list x y) (list :int #'* :int :int)))
+ (:op #\/ 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)))
+ (:op #\+ binop "+" (x y 5)
+ (dispatch "+" (list x y) (list :int #'+ :int :int)))
+ (:op #\- binop "-" (x y 5)
+ (dispatch "-" (list x y) (list :int #'- :int :int))))
+
+ ((:op #\+ preop "+" (x 9)
+ (dispatch "+" (list x) (list :int #'+ :int)))
+ (:op #\- preop "-" (x 9)
+ (dispatch "-" (list x) (list :int #'- :int)))
+ (:op #\( lparen #\)))
+
+ ((: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.
~mdw / sod / blobdiff