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

[Twylite <tw...@cr...>]

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?

One can construct other ambiguities that exploit the inability to 
distinguish between a pattern for a pluggable matcher (i.e. you can't 
make assumtions about what is and isn't a valid input) and the keywords 
of the [try] itself.

Regards,
Twylite