Re: [TCLCORE] handling loops interruption within a 'try'

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

The original code doesn't work because [while] converts TCL_BREAK into TCL_OK (or is bytecode-compiled to something equivalent). By the time it gets to the [try], it's already gone. Differentiating these is a sufficiently unusual requirement that we have no explicit support for it.

Donal.

-------- Original message --------
From: Csaba Nemethi <csa...@t-...>
Date: 01/04/2025 15:21 (GMT+00:00)
To: tcl...@li...
Subject: Re: [TCLCORE] handling loops interruption within a 'try'

The following *restructured* code works for me as expected:


proc p {}
     while {[some_expensive_query]} {

         # ....

         if {[some_intervening_condition]} {
             return -code break ;# -level 1
         }

         # ....
     }
}

try {
     p
} on break {} {
     puts " ---- break ----"
     puts "Loop interrupted by break"
} on ok {} {
     puts "Loop completed normally"
} finally {
     puts "done"
}


Am 01.04.25 um 07:27 schrieb Massimo Manghi:
> I apologize for (ab)using this mailing list to ask a question that maybe
> has a trivial answer.
>
> I just can't have the 'on break' clause be triggered in a loop
> controlled by a 'try' construct
>
> try {
>      while {[some_expensive_query]} {
>
>          # ....
>
>          if {[some_intervening_condition]} {
>              return -code break -level 0
>          }
>
>          # ....
>      }
> } on break {} {
>      puts " ---- break ----"
>      puts "Loop interrupted by break"
> } on ok {} {
>      puts "Loop completed normally"
> } finally {
>      puts "done"
> }
>
> and you have a normal termination even though the loop was interrupted
> prematurely by [some_intervening_condition]
>
> I can get what I want by raising an exception with 'throw' and then
> using the trap clause which allows extra control over the cause of the
> exception (-errorcode receives no special treatment unless the option -
> code error is passed) but what is the purpose of the 'on break' clause
> if it's not handling a break?
>
>   -- Massimo
>
>
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--
Csaba Nemethi  https://urldefense.com/v3/__https://www.nemethi.de__;!!PDiH4ENfjr2_Jw!HEnJRLIzKYhQhoP6uLmD3-X_vyVjELprni_4haY-9QlMVUvAsyae59IdzAhgOQCvj9KRwmBTjlRcm33Vj8Nf9D110XEqyXSCAsaHg4WY$[nemethi[.]de]  mailto:csa...@t-...



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