Re: Exception handling within a compound statement?

[Gaius Mulley]

"Fischlin  Andreas" <andreas.fischlin@env.ethz.ch> writes:

> Dear Phil,
>
> Modula-2 has the philosophy of handling errors explicitly as the programer 
> strives to write an error free code in the first place. The only exceptions 
> that can
> be considered are numerical ones, such as an integer or real overflow etc., 
> which are detected and handled by the underlying hardware and system settings.
> Depending on the current setting for the handling of such exceptions 
> (tolerate or respond etc.) this results typically in a HALT of the Modula-2 
> program with
> some information on the causes of the exception and/or triggering of a 
> debugger.
>
> Hope this helps.
>
> Sincerely yours,
> Andreas Fischlin
>
> ETH Zurich
> Prof. em. Dr. Andreas Fischlin
> Systems Ecology - Institute of Biogeochemistry and Pollutant Dynamics
> CHN E 24
> Universitaetstrasse 16
> 8092 Zurich
> SWITZERLAND
>
> andreas.fischlin@env.ethz.ch
> https://sysecol.ethz.ch/people/andreas.fischlin.html
>
> +41 44 633-6090 phone
> +41 79 595-4050 mobile
>
>              Make it as simple as possible, but distrust it!
> ________________________________________________________________________
>
>  On 20 Dec 2023, at 04:20, Philip Munts <phil@munts.net> wrote:
>
>  Ada allows exception handling within each begin/end block, and
>  also allows a begin/end block inside a compound statement:
>
>  loop
>   begin
>     raise Program_Error;
>   exception
>     when Program_Error =>
>       ...
>   end;
>  end loop;
>
>  Does GM2 allow something similar, or can exceptions be caught
>  only at the procedure or module level?
>
>  I like to use exceptions to propagate errors in Ada embedded
>  real-time software, since they can be caught and handled
>  anywhere along the calling chain or just ignored to abort the
>  program.
>
>  If exceptions can only be caught at procedure or module level
>  on the way out to a program abort, they are much less useful
>  to me.
>
>  Phil

Hi Andreas and Phil,

very true for pim[234] (I guess on some systems nil violation might be
caught by the underlying platform?).  In iso exceptions are allowed but
only in the begin end blocks of modules and procedures.

An interesting exception example from the iso standard can be found in:

   gcc/testsuite/gm2/iso/run/pass/except8.mod

   
http://cvs.savannah.nongnu.org/viewvc/gm2/testsuite/gm2/iso/run/pass/except8.mod?view=markup

(not that I'm advocating writing code like this :-).  On a more
practical note the exception handling scheme works well and across
languages - and if using swig across into scripting languages. (Python3
can catch a m2 exception).  In gm2 the procedure THROW is available from
the SYSTEM module and can be invoked from anywhere,

regards,
Gaius