Re: Error Handling
Excellent David. Exception handling under the control of the application is
the highest priority enhancement required in Euphoria, then comes namespace
resolution, and the 'C' translator is not a priority at all for me.
If I can add to David's excellent suggestion (quoted in full below), the
application might need to know exactly which exception occurred to trigger
the "on error do" block. So something like Basic's "err" or C's "errno"
could be set by Euphoria just prior to invoking the "on error" block. Also,
the code in there might need a way to resume execution or to retry the
statement that caused it. This is sounding a lot like Basic's error handling
now. But a "resume" and a "retry" statement could be needed.
Still another idea would be to allow application generated exceptions to be
handled in the same manner. Maybe via a "raise <exceptionnumber>" statement.
------
Derek Parnell
Melbourne, Australia
"To finish a job quickly, go slower."
----- Original Message -----
From: "David Cuny" <dcuny at LANSET.COM>
> I had written a simple Windows game, and was showing it off to various
> people. Naturally, it crashed and burned - especially on NT machines. Up
> popped the console, spewing a traceback, and an EX.ERR appeard on the
> desktop. While this information was useful to me, it's not the sort of
thing
> I'd want the user to ever see.
>
> I've written another small Euphoria program that will be used in front of
my
> entire division. I'd hate to see it go down in flames in front of all
those
> people. Naturally, I've checked it for errors, but I'm no Knuth - there
are
> bound to be error lurking in the code.
>
> For this reason, I never use Euphoria's custom types. It's akin to using
> ASSERTS in C - great for testing code, but you don't want them in the
> release code. Euphoria has all these great tools for catching bugs - but
> nothing for recovering from them at runtime.
>
> This is a Bad Thing, because it leads to people losing their work, or
> programs stopping which could potentially recover.
>
> In contrast, almost all the 'modern' languages (such as Java or Python)
have
> some sort of try/fail mechanism. Heck, even QBasic has an ON ERROR
> statement. While I've never really been a fan of this sort of thing, it
> serves an important function: it makes better code.
>
> In the past, I've lobbied for something like this:
>
> crash_routine = routine_id("MyCrashRoutine")
>
> This way, you could at least save the user's valuable data, so they don't
> lose all their work.
>
> I still think this sort of thing would be good, but I think we can do
> better. Imagine that we had a 'on error' routine for functions and
> procedures. If a 'fatal' error is encountered, Euphoria branches to that
> clause:
>
> function my_function
> -- code goes here
> on error do
> -- recover from error
> end procedure
>
> If there were no recovery routine for the current routine, Euphoria pop
it's
> return stack until it encountered one. So if there were no recovery
routines
> at all, it would simply fail as it currently does. If you wanted to be
lazy
> (like me), you could just put a single recovery routine in the top level
> procedure:
>
> procedure main()
> -- code goes here
>
> on error do
> -- save the data file and shut down
>
> end procedure
>
> Unlike crash_routine, the 'on error' clause would allow the routine to
> recover from the error. This means that programs wouldn't come crashing to
a
> halt. You could control exactly how fine a level of control you wanted.
>
> Comments?
>
> -- David Cuny
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