Re: [TCLCORE] TIP#239 Try/Catch/Finally syntax [WAS Re: Tcl-Core Digest, Vol 30, Issue 10]

[Donal K. F. <don...@ma...>]

Neil Madden wrote:
> I believe this is already addressed by the presence of errorCode. 
> Pattern-matching against this code is already quite simple, with 
> [switch] and so on. It just hasn't caught on. It seems like wishful 
> thinking to expect that it will suddenly catch on just because its usage 
> is made slightly more convenient (we're talking about a reduction of 
> about 1 line of code).

Also a reduction in the nesting depth. That reduces user-visible
complexity. That's a good bonus.

> 4. Trapping only those errors/exceptions you are interested in
> --------------------------------------------------------------
> 
> It's clear from the above that the Twylite/JE approach achieves this for 
> errors, but not for other exceptions. My approach achieves it for 
> exceptions but not for more specific error cases.

The problem with making more use of exception codes is that they're a
global resource; they're not easy to restrict to a single interpreter.
That makes them significantly less suitable for use in packages, and
hence restricts their general applicability rather a lot. They've also
got hard-coded traceability behaviour (i.e. none).

> Branching based on the result just seems like a fragile nightmare. 
> Localised error messages for instance could totally change the behaviour 
> of code.

Agreed. And localizing error messages is messy too without in effect the
effort required to generate errorcodes properly. Which in turn makes the
error trapping proposed viable and useful. :-)

Donal.