Errors are reported to the user by an error display handler that is called by the default exception handler (see section 2.23). The argument to the error display handler is a complete error message to be displayed. The default error display handler displays its argument to the current error port.
Generally, the error display handler is only called directly by an exception handler. To report a run-time error, use raise (see section 2.23) or error (see section 2.24) instead.
If an exception is raised while the error display handler is executing, an error message is printed using a primitive error printer and the primitive error escape handler is invoked.