TACL Reference Manual

Built-In Functions and Variables

HP NonStop TACL Reference Manual—429513-018

9-179

#FILTER Built-In Function

Use #FILTER in a routine to specify the exceptions the routine can handle. An

exception is an unusual event that causes TACL to interrupt the normal flow of

invocations and transfer to special code, known as an exception handler. The event

can be BREAK, a TACL error, or a user-defined exception.

exception

is the name of an unusual event, which can be any of these:

_BREAK

specifies that the BREAK key is to be handled as an exception, when pressed.

_ERROR

specifies that errors detected by TACL are to be handled. In addition, your

code can explicitly raise this exception.

user-exception

specifies a user-defined routine that can be invoked by #RAISE, causing the

routine that handles #FILTER to be reinvoked and to set #EXCEPTION to

user-exception.

Result

#FILTER returns nothing.

Considerations

•

A portion of a TACL program that performs the actions required by one or more

exceptions is known as an exception handler. An exception handler must do the

following, within a routine:

Include a #CASE built-in function call to handle each of the exceptions the

handler supports. The #EXCEPTION built-in function returns the type of

exception that invoked the handler; use it to direct the #CASE function.

Specify names of exceptions supported by the handler. For this step, use the

#FILTER built-in function to specify the exceptions. TACL does not invoke an

exception handler for an exception unless it is listed in the #FILTER list.

If your code contains these two items and an exception occurs while one of your

functions is executing, the TACL process will invoke the #EXCEPTION built-in function

with the name of the exception that occurred.

#FILTER [ exception [ exception ] ... ]