Error Handling/Reporting Cycle

The warning system was designed to work in conjunction with several layers of CALLed programs. If an error occurs in a program that was CALLed by another program, the program with the error should call _warn.utl with an initial indication of an error. It should then exit with an error status, causing a trap to the error routine of the program that called it. For example, consider the following programs A, B, and C:

Program A:
SETERR DO_ERROR
LET BBEXT$=STBL("BBEXT")
...
CALL "B"
...
END
DO_ERROR:
IFERR<>200THENCALL BBEXT$+"_unerr.utl",
 ERR,TCB(5),PGM(-2),TCB(10)
CALL BBEXT$+"_warn.utl",
 "Critical Application Failure:"
CALL BBEXT$+"_saywarn.utl"
END

Assume that the user RUNs program A. Program A CALLs program B, which CALLs program C. Program C generates an !ERROR=41, causing control to go to the Program C error routine. Because !ERROR=41, the program should call the _unerr.utl utility, loading the warning buffer with the following:

Unexpected Error:
An invalid integer was detected
at line 30 in module C.
Program B:
SETERR DO_ERROR
LET BBEXT$=STBL("BBEXT")
…
CALL "C"
…
EXIT
DO_ERROR:
IF ERR<>200THENCALL BBEXT$+"_unerr.utl",
  ERR,TCB(5),PGM(-2),TCB(10)
CALL BBEXT$+"_warn.utl",
  "Program B can not continue:"
EXIT (200)

Program C:
SETERR DO_ERROR
LET BBEXT$=STBL("BBEXT")
...
A$=A$(-1); REM Generate an !ERROR=41
...
EXIT
DO_ERROR:
 IF ERR<>200 THEN CALL
BBEXT$)+"_unerr.utl",
  ERR,TCB(5),PGM(-2),TCB(10)
 CALL BBEXT$+"_warn.utl",
  "Program C can not continue:"
EXIT(200)

Program C adds an additional line to the warning buffer:

Program C can not continue:
Unexpected Error:
An invalid integer was detected
at line 30 in module C.

Program C then exits to program B with an error condition. Typically, this is EXIT 200. Program B executes its error handler and adds a line to the warning buffer:

Program B can not continue:
Program C can not continue:
Unexpected Error:
An invalid integer was detected
at line 30 in module C.

Next, program B exits to program A with an error condition, EXIT 200, and Program A invokes its error routine creating the following warning buffer:

Critical Application Failure:
Program B can not continue:
Program C can not continue:
Unexpected Error:
An invalid integer was detected
at line 30 in module C.

This is displayed on the screen because Program A calls _saywarn.utl.

The warning message shows exactly why the application failed: Program B had a failure because Program C had a failure. From top to bottom, the error message gets more specific about the actual cause of the failure.