OpenEuphoria

exception handler

• Posted by Robert Craig <rds at RapidEuphoria.com> Aug 24, 2004
• 686 views

I'm ready to implement the global exception handler concept.
This will give your program a chance to take some action
when the Euphoria interpreter (or less common - translated code) 
detects a run-time error. In 2.5 your program is completely parsed
(compiled) before any execution begins, so there isn't much 
value in being able to react to compile-time errors.
The implementation of this thing probably won't be difficult,
but I want to get the language design right.

I'm assuming the following:

   * using routine id's you can specify one or more routines 
     to receive control when a run-time error occurs. Allowing 
     more than one routine would be useful for library writers 
     who might want to specify a routine to clean up resources, 
     locked files etc. for their library, independent of what 
     the application writer wants to do in his own code.

   * you can't resume execution. Once the crash routine(s)
     have finished, the program will terminate.

   * by default, the most recently specified crash routine will
     be executed first, working back to the first routine
     specified. Maybe there will be a way to change this order.

   * your routine(s) will be called after the normal ex.err dump
     occurs, so I guess your routine(s) could look at ex.err
     in deciding what to do. If a second ex.err is necessary
     while running your routines, I'll use a different file name, 
     like ex2.err or something. If your routine(s) themselves crash, 
     there won't be any more calls to crash routines. That's the end.

The possible uses for this have been discussed before.
e.g. 
   - cleaning up files and resources that won't automatically be 
     cleaned up when the interpreter terminates your program.

   - the "classic" example of an editor that could save the
     user's edit buffer to disk before dying.

   - a server program that could send an e-mail notification
     with debug info (such as ex.err) when it dies unexpectedly 
     in the middle of the night.

   - I suppose a program could effectively restart itself 
     and keep going if a crash routine were set up that way.

Regards,
   Rob Craig
   Rapid Deployment Software
   http://www.RapidEuphoria.com