pTAL Reference Manual (H06.08+)

Statements
HP pTAL Reference Manual—523746-006
12-25
GOTO and Target Statements With Different
Trapping States
If a GOTO statement and the target statement are in different BEGIN-END blocks:
•
You must declare the target label in a LABEL declaration in the containing
procedure.
•
Overflow trapping must be enabled in both blocks or disabled in both blocks. The
respective overflow trapping states can be established by compiler directive, by
procedure attribute, or by BEGIN-END block attribute.
•
A GOTO statement in a BEGIN-END block that does not specify a block-level
trapping attribute cannot branch to a label in a BEGIN-END block in which a block-
level trapping attribute is specified.
The compiler uses attributes on BEGIN-END blocks to determines whether a GOTO
within one BEGIN-END block can branch to a label in another BEGIN-END block.
For more information, see Section 13, Hardware Indicators.
Note. LABEL is an invalid data type for a formal parameter. You cannot pass a label as an
actual parameter.
Example 12-24. Nonlocal GOTO and Target Statements That Have Different
Trapping States
PROC p OVERFLOW_TRAPS;
BEGIN
INT i := 0;
label_a: ! Overflow traps are enabled at label_a
i := i + 1;
IF i < 10 THEN
GOTO label_a ! OK: Traps enabled here and at label_a
ELSE
BEGIN:ENABLE_OVERFLOW_TRAPS
GOTO label_a; ! OK: Branch from block with traps
IF i <> 1 THEN ! specified
BEGIN
label_b: ...
END;
END;
BEGIN:DISABLE_OVERFLOW_TRAPS
GOTO label_b; ! ERROR: Cannot branch between blocks
END; ! that have different trapping states
BEGIN
GOTO label_b; ! ERROR: Cannot branch from a BEGIN-END
END; ! block that does not specify a trapping
END; ! attribute to a BEGIN-END block that
! does