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From: tmcclory@wright.EDU (Tom McClory)
Newsgroups: comp.lang.ada
Subject: Novice Questions on Ada Exceptions
Keywords: PROGRAM_ERROR exceptions debugging maintenance
Message-ID: <620@thor.wright.EDU>
Date: 21 Aug 89 01:22:13 GMT
Organization: Wright State University, Dayton OH, 45435
List-Id: <comp.lang.ada>


I am attempting to port the Ada Test an Analysis Tools package, 
(contributed by Intermetrics to the Ada Repository) to the UNIX 
operating system using the Verdix Ada Compiler (release 5.4).  
The package compiled with no obvious errors, and what appear 
to be minor warnings.  However, the program fails during 
operation with the following exception message:

** MAIN PROGRAM ABANDONED -- EXCEPTION "program_error" RAISED

The VADS debugger sheds a little more light on this with the
output:

RM 11.3(3): RAISE statement reraised exception

This leads to several questions . . .

1) Does anyone have experience porting/using this "Ada Test
and Analysis Tools" package from the Ada Repository?  Are there 
any configuration issues I may have missed?  The changes I made 
were to define a type "long float" and to fix a few typographical 
errors (missing spaces) that may have been introduced during upload.

2) A more general question . . . what are typical causes for 
"PROGRAM_ERROR" exceptions?  More specifically, what might be causing
this error?  The text book I'm using (_Understanding Ada_, by 
Bray & Pokrass, 1985) mentions only "leaving a function without 
executing a return statement."  (Won't the compiler catch these?)

3) Even more general . . . what are good strategies for tracking the
source of exceptions in large programs you personally didn't write?
The behavior of the VADS debugger during exception handling seems 
shaky (I get warning messages about loosing track of pointers), 
so I don't trust the information I've gotten.  Neither the error 
message, nor the debugger, accurately pinpoint the source of the 
exception.  Rather, the debugger states "exception raised xxx 
instructions beyond the statement shown", which is the last 
statement in the last block of whatever file happened to be displayed 
when the exception triggered.  

Any suggestions are welcomed.  Thanks in advance.