Lexical Elements of the DEC Text Processing Utility Language 4.9 Reserved Words

Example 4–11 Procedure with a Case-Style Error Handler

PROCEDURE eve$learn_abort

ON_ERROR [TPU$_CONTROLC]:

MESSAGE (ERROR_TEXT); RETURN (LEARN_ABORT);

ENDON_ERROR;

IF LEARN_ABORT THEN

eve$message (EVE$_LEARNABORT); RETURN (TRUE);

ELSE

RETURN (FALSE);

ENDIF;

ENDPROCEDURE;

If a program or procedure has a case-style error handler, DECTPU handles errors and warnings as follows:

•If you press Ctrl/C, DECTPU determines whether the error handler contains a selector labeled TPU$_CONTROLC. If so, DECTPU sets ERROR to TPU$_ CONTROLC, ERROR_LINE to the line that DECTPU was executing when Ctrl/C was pressed, and ERROR_TEXT to the message associated with TPU$_ CONTROLC. DECTPU then executes the statements associated with the selector. If there is no TPU$_CONTROLC selector, DECTPU exits from the error handler and looks for a TPU$_CONTROLC selector in the procedures or program (if any) in which the current procedure is nested. If no TPU$_ CONTROLC selector is found in the containing procedures or program, DECTPU places the message associated with TPU$_CONTROLC in the message buffer.

•If an error or warning is generated during a CALL_USER routine, ERROR is set to a keyword that represents the failure status of the routine, ERROR_ LINE is set to the line number of the error, and ERROR_TEXT is set to the warning or error message associated with the keyword. DECTPU then processes the error handler that trapped the CALL_USER error in the same way that DECTPU processes normal case-style error handlers.

•For other warnings and errors, ERROR is set to a keyword that represents the error or warning, ERROR_LINE is set to the line number of the error, and ERROR_TEXT is set to the error or warning message associated with the keyword.

The way a case-style error handler processes an error or warning depends on how the error handler traps the error. There are three possible ways, as follows:

–The error handler can trap the error by using a selector that matches the error exactly (that is, using a selector other than OTHERWISE).

–The error handler can trap the error by using the OTHERWISE selector.

–The error handler can completely fail to trap the error.

The following discussion explains how a case-style error handler processes an error or warning in each of these circumstances.

4–26Lexical Elements of the DEC Text Processing Utility Language

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Compaq AA-PWCBD-TE manual Example 4-11 Procedure with a Case-Style Error Handler
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