Making An Error Trap - HP 48gII Advanced User's Reference Manual

Key Programmable
Command
!° L L %ERROR% :
DOERR
%DOERR%
ERNN
%ERRN%
ERRM
%ERRM%
ERR0
%ERR0%

Making an Error Trap

You can construct an error trap with one of the following conditional structures:
IFERR ... THEN ... END.
!
IFERR ... THEN ... ELSE ... END.
!
The IFERR ... THEN ... END Structure
The syntax for this structure is
« ... IFERR trap-clause THEN error-clause END ... »
The commands in the error-clause are executed only if an error is generated during execution of the trap-clause.
If an error occurs in the trap-clause, the error is ignored, the remainder of the trap-clause is skipped, and
program execution jumps to the error-clause. If no errors occur in the trap-clause, the error-clause is skipped and
execution resumes after the END command.
To enter IFERR ... THEN ... END in a program:
Press !°LL %ERROR% !%IFERR%.
!
Example: The following program takes any number of vectors or arrays from the stack and adds them to the
statistics matrix. However, the program stops with an error if a vector or array with a different number of
columns is encountered. In addition, if only vectors or arrays with the same number of columns are on the stack,
the program stops with an error after the last vector or array has been removed from the stack.
« WHILE DUP TYPE 3 == REPEAT ...+ END »
In the following revised version, the program simply attempts to add the level 1 object to the statistics matrix
until an error occurs. Then, it ends by displaying the message DONE.
Error Trapping Commands
Causes an error. For a string in level 1, causes a user-defined error: the
calculator behaves just as if an ordinary error has occurred. For a binary
integer or real number in level 1, causes the corresponding built-in error.
If the error isn't trapped in an IFERR structure, DOERR displays the
message and abandons program execution. (For 0 in level 1, abandons
execution without updating the error number or message — like −.)
Returns the error number, as a binary integer, of the most recent error.
Returns #0 if the error number was cleared by ERR0.
Returns the error message (a string) for the most recent error. Returns
an empty string if the error number was cleared by ERR0.
Clears the last error number and message.
Description
RPL Programming 1-33