Handling Errors in a VLX Application Running in Its Own Namespace

For VLX applications executing within their own namespace, you can either use the default error function or you can define an error handler specifically for the application.

If you define an error handler for a VLX running in its own namespace, you can call the vl-exit-with-error function to pass control from the VLX error handler to the document namespace's *error* function. The following example uses vl-exit-with-error to pass a string to the document's *error* function:

(defun *error* (msg)
  ... ; processing in VLX namespace/execution context
(vl-exit-with-error (strcat "My application bombed! " msg)))

A VLX *error* handler can use the vl-exit-with-value function to return a value to the document namespace from which the VLX was invoked. The following example uses vl-exit-with-value to return the integer value 3 to the program that called the VLX from the document namespace:

(defun *error* (msg)
  ... ; processing in VLX-T namespace/execution context
  (vl-exit-with-value  3))
(vl-doc-export 'foo)
(defun foo (x)
  (bar x)
  (print 3))
(defun bar (x) (list (/ 2 x) x))

Any instructions pending at the time the error occurred are flushed.

If your VLX namespace error handler does not use either vl-exit-with-error or vl-exit-with-value, then control returns to the command prompt after execution of the error handler. You can only call vl-exit-with-error and vl-exit-with-value in the context of a VLX application's error handler; it is an error to invoke these functions in any other situation.