RE: monitor for exception by message id

Hello Buck,

You wrote:
>Well, sort of.  The way most OS/400 processes do this is to send up some
>diagnostics, then the escape message.  It's up to the message handler to
>read the diagnostics.  I understand where you're coming from: it isn't the
>same as other platforms.

That's because the AS/400 is better than the other platforms. The exception 
message model is a very advanced way of interacting between caller and 
callee. We've had it for over 30 years. Smalltalk has it, C++ stole it and 
Java cloned it. Like so much of what the AS/400 has, it doesn't get any 
credit for it because it's different from what others do. Different <> 
Wrong. Different -> Better.

>In my own stuff, I don't actually throw escape messages to the caller.
>Rather, I set a return code that the caller needs to inspect.  I stick my
>return codes in a /COPY member and refer to them via mnemonics rather than
>by number.  I'm not sure if this helps or not...

Return codes have their place but in my view the exception model is far 
superior. That is because a return code can be ignored by the caller but an 
exception cannot. Unix is a prime example of an environment where return 
codes are used and frequently never checked because "that error will never 
happen" and "error handling code makes the program slow" and other lame 
Unix-weenie excuses. An exception model forces the caller to deal with the 
error. Of course they can simply monitor and ignore (like MONMSG CPF0000) 
but that requires an overt action on the part of the caller rather than an 
error of omission.

The exception model is certainly more expensive than the return code model 
(both in terms of programmer skill and system resources) but, like most 
things, you get what you pay for.

Regards,
Simon Coulter.
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