MONITOR (Begin a Monitor Group)

The monitor group performs conditional error handling based on the status code. It consists of:

• A MONITOR statement
• One or more ON-ERROR groups
• An ENDMON statement.

After the MONITOR statement, control passes to the next statement. The monitor block consists of all the statements from the MONITOR statement to the first ON-ERROR statement. If an error occurs when the monitor block is processed, control is passed to the appropriate ON-ERROR group.

If all the statements in the MONITOR block are processed without errors, control passes to the statement following the ENDMON statement.

The monitor group can be specified anywhere in calculations. It can be nested within IF, DO, SELECT, or other monitor groups. The IF, DO, and SELECT groups can be nested within monitor groups.

If a monitor group is nested within another monitor group, the innermost group is considered first when an error occurs. If that monitor group does not handle the error condition, the next group is considered.

Level indicators can be used on the MONITOR operation, to indicate that the MONITOR group is part of total calculations. For documentation purposes, you can also specify a level indicator on an ON-ERROR or ENDMON operation but this level indicator will be ignored.

Conditioning indicators can be used on the MONITOR statement. If they are not satisfied, control passes immediately to the statement following the ENDMON statement of the monitor group. Conditioning indicators cannot be used on ON-ERROR operations individually.

If a monitor block contains a call to a subprocedure, and the subprocedure has an error, the subprocedure's error handling will take precedence. For example, if the subprocedure has a *PSSR subroutine, it will get called. The MONITOR group containing the call will only be considered if the subprocedure fails to handle the error and the call fails with the error-in-call status of 00202.

The monitor group does handle errors that occur in a subroutine. If the subroutine contains its own monitor groups, they are considered first.

Branching operations are not allowed within a monitor block, but are allowed within an ON-ERROR block.

A LEAVE or ITER operation within a monitor block applies to any active DO group that contains the monitor block. A LEAVESR or RETURN operation within a monitor block applies to any subroutine, subprocedure, or procedure that contains the monitor block.

For more information, see Error-Handling Operations.

 * The MONITOR block consists of the READ statement and the IF
 * group.
 * - The first ON-ERROR block handles status 1211 which
 *   is issued for the READ operation if the file is not open.
 * - The second ON-ERROR block handles all other file errors.
 * - The third ON-ERROR block handles the string-operation status
 *   code 00100 and array index status code 00121.
 * - The fourth ON-ERROR block (which could have had a factor 2
 *   of *ALL) handles errors not handled by the specific ON-ERROR
 *   operations.
 *
 * If no error occurs in the MONITOR block, control passes from the
 * ENDIF to the ENDMON.
C                  MONITOR
C                  READ       FILE1
C                  IF         NOT %EOF
C                  EVAL       Line = %SUBST(Line(i) :
C                                           %SCAN('***': Line(i)) + 1)
C                  ENDIF
C                  ON-ERROR   1211
C                   ... handle file-not-open
C                  ON-ERROR   *FILE
C                   ... handle other file errors
C                  ON-ERROR   00100 : 00121
C                   ... handle string error and array-index error
C                  ON-ERROR
C                   ... handle all other errors
C                  ENDMON