Summary:

I've found the following:

% puts stdout [catch {incr i}]
0 % puts stdout [catch {error foo}]
1 % puts stdout [catch {return foo}]
2 % puts stdout [catch {break}]
3 % puts stdout [catch {continue}]
4

Which is all as expected and documented.

However

% puts stdout [catch {return -code ok}]
2 % puts stdout [catch {return -code error}]
2 % puts stdout [catch {return -code return}]
2 % puts stdout [catch {return -code break}]
2 % puts stdout [catch {return -code continue}]
2

I'd expect these to return 0, 1, 2, 3 and 4 as in the previous case.

What am I missing?

Background:

I'm doing some web scraping and I want to check if something has
appeared on the page, if so, I'm done, otherwise I want to pause and
retry a few times, and if it's not there at the end there's an error.
So, I'm trying to develop a new control structure of the form

proc wait {testScript} {backoff script} {timeoutScript} {
.
.
.
}

I want to return some application-specific information from the
timeoutScript, and I've been trying to do so via [return -code error],
but the error isn't being propagated to the code that calls wait because
timeoutScript is using return -code error -errorinfo {...} {other
stuff}. I've changed this to error {other stuff} {...} and my code in
[wait] works as I want it to, but the return manpage seems to suggest
using [return] rather than [error].

I'm using tcl 8.6.9 from ActiveTcl and testing with tkcon.

Alan

The -code option value has to be interpreted in conjunction with the
-level option which defaults to 1.

% puts [catch {return -code error -level 0}]
1 % puts [catch {return -code break -level 0}]
3 % puts [catch {return -code continue -level 0}]
4

Without the -level 0, the codes are seen one level up the stack
(defaulting to -level 1), not by the return invocation itself.

% proc xx {} {return -code break} ; # Defaults to -level 1
% catch {xx}
3 % proc yy {} {return -code break -level 2}
% proc zz {} {yy}
% catch yy
2 % catch zz
3

/Ashok

On 8/18/2022 2:58 AM, Alan Grunwald wrote:
> Summary:
>
> I've found the following:
>
> % puts stdout [catch {incr i}]
> 0
> % puts stdout [catch {error foo}]
> 1
> % puts stdout [catch {return foo}]
> 2
> % puts stdout [catch {break}]
> 3
> % puts stdout [catch {continue}]
> 4
>
> Which is all as expected and documented.
>
> However
>
> % puts stdout [catch {return -code ok}]
> 2
> % puts stdout [catch {return -code error}]
> 2
> % puts stdout [catch {return -code return}]
> 2
> % puts stdout [catch {return -code break}]
> 2
> % puts stdout [catch {return -code continue}]
> 2
>
> I'd expect these to return 0, 1, 2, 3 and 4 as in the previous case.
>
> What am I missing?
>
>

Thanks Ashok,

That has certainly fixed my problem.

I guess the problem is that the code with the 'return' in it is executed
via uplevel rather than some variety of call. I suppose the lesson is
that this is pushing my understanding of Tcl to its limits.

Thanks again,

Alan

On 18/08/2022 02:31, apn wrote:
> The -code option value has to be interpreted in conjunction with the
> -level option which defaults to 1.
>
> % puts [catch {return -code error -level 0}]
> 1
> % puts [catch {return -code break -level 0}]
> 3
> % puts [catch {return -code continue -level 0}]
> 4
>
> Without the -level 0, the codes are seen one level up the stack
> (defaulting to -level 1), not by the return invocation itself.
>
> % proc xx {} {return -code break} ; # Defaults to -level 1
> % catch {xx}
> 3
> % proc yy {} {return -code break -level 2}
> % proc zz {} {yy}
> % catch yy
> 2
> % catch zz
> 3
>
> /Ashok
>
> On 8/18/2022 2:58 AM, Alan Grunwald wrote:
>> Summary:
>>
>> I've found the following:
>>
>> % puts stdout [catch {incr i}]
>> 0

<snip>

>>
>> Which is all as expected and documented.
>>
>> However
>>
>> % puts stdout [catch {return -code ok}]
>> 2

<snip>

>>
>> What am I missing?
>>
>>
>

Just to not limiting yourself:
https://www.magicsplat.com/ttpl/index.html