-
- (labels ((type-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))))
- (add (x y) (type-dispatch "+" (list x y)
- (list :integer #'+ :integer :integer)))
- (sub (x y) (type-dispatch "-" (list x y)
- (list :integer #'- :integer :integer)))
- (mul (x y) (type-dispatch "*" (list x y)
- (list :integer #'* :integer :integer)))
- (div (x y) (type-dispatch "/" (list x y)
- (list :integer
- (lambda (x y)
- (cond ((zerop y)
- (cerror*
- "Division by zero")
- (cons :invalid nil))
- (t
- (floor x y))))
- :integer :integer)))
- (nop (x) (type-dispatch "+" (list x)
- (list :integer #'+ :integer)))
- (neg (x) (type-dispatch "-" (list x)
- (list :integer #'- :integer))))
-
- (with-parser-context (token-scanner-context :scanner scanner)
- (parse (expr (lisp (flet ((prop (type value)
- (scanner-step scanner)
- (values (cons type value) t t)))
- (case (token-type scanner)
- (:int
- (prop :integer (token-value scanner)))
- ((:id :char :string)
- (prop (token-type scanner) (token-value scanner)))
- (#\?
- (let* ((stream (make-scanner-stream scanner))
- (sexp (read stream t)))