Re: [TCLCORE] TIP#239 Try/Catch/Finally syntax

[Neil M. <ne...@Cs...>]

On 22 Nov 2008, at 23:42, Twylite wrote:
> Hi,
>> try ?-matchcommand cmd? script ?handlers ...? ?finally script?
>>
>> Where -matchcommand is the command to use to do errorCode matching
>> and defaults to {switch -glob --}. (May need a -- marker to eliminate
>> ambiguity). The syntax of the handlers part would be:
>>
>> on exception-types ?vars? ?errorPattern? body ?errorPattern
>> body ...?
> I'm very uncomfortable with this syntax.  It is potentially ambiguous
> and feels very DWIMy (in a bad way).
>
> try {
>   # do stuff
> } on error {
>   puts hello
> } finally {
>   puts goodbye
> }
>
> ... is ambiguous.  It could be interpreted the way you think, or with
> "puts hello" as the vars and "finally" as the error pattern.
>
> Consider also:
> try { ... } on error {em opts} "POSIX *" { body } on break
>
> Is "on break" an errorPattern and body, or the start of a new  
> exception
> handler?

I don't think it's possible to avoid ambiguity while still preserving  
ease of use. The alternative is to make less things optional, which  
just becomes a pain. My preference is to make "on" a keyword in this  
context. It's highly unlikely that a script or a variable would just  
be named "on", and if we document this as a keyword in this context  
then there should be no problem.

-- Neil

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