例.restart-case,handler-bind ,handler-case

restart-case,handler-bind用法。

 樣例代碼：

(defun get-age (text)
    (restart-case
        (cond
            ((symbolp text) (error 'invalid-integer :msg "Invalid integer"))
            ((and (stringp text) (loop for x across text always (digit-char-p x)))
                (parse-integer text :junk-allowed nil))
            ((eq (type-of text) (type-of 2)) text)
            (t
                (error 'invalid-integer :msg "Invalid integer2")))
        (use-value (val) val)
        (retry-parse (text) (get-age text))))

(define-condition invalid-integer (error)
            ((msg :initarg :msg
                :reader msg)))
                
(defun retry-parse (text)
    (let ((restart (find-restart 'retry-parse)))
        (when restart
            (invoke-restart 'retry-parse text))))

(defun test-1 (text default-value)
    (handler-bind 
        ((invalid-integer #'(lambda (e)
                (format t "error msg:~a~%" (msg e))
                    (let ((it (find-restart 'use-value)))
                     (when 
                        (invoke-restart it default-value)))))
        (error (lambda (e)
            (print e)
            (retry-parse default-value))))
        (get-age text)))
        
        
; (test-1 "as33" 34)
; (test-1 33 34)
; (test-1 'a 34)
; (test-1 "33" 34)