Re: [TCLCORE] [Ext] Re: TIP 672 Implementation Complete - Ready for Sponsorship

[EricT <tw...@gm...>]

Hi Kevin:

Yes, the main breakage issue is the empty array case that's been discussed
extensively here.

When I wrote the TIP, it was originally targeted for 9.0 when breaking
changes were permitted. It got bumped to 9.1, though I didn't change that
myself.

The real innovation here is the parser injection point that enables
multiple syntaxes with minimal code changes. Three are being considered:

$(...) - Cleanest syntax, but conflicts with empty array shortcut $(index)
$=(...) - Virtually no conflicts - literal $=( is extremely rare without
escaping \$=(
$((...)) - Also conflicts with empty arrays when index starts with ( like
$((index)

My prototype already implements the first two; someone else is working on
the third. The extremely minor conflicts in options 2 and 3 are unlikely to
affect real code.

The choice is up to the core team. Having a working C implementation helps
inform that decision. I hope to earn your yes vote, and I'm happy to answer
any questions.


On Thu, Oct 23, 2025 at 4:42 AM Kevin Walzer <kw...@co...> wrote:

> Hi Eric,
>
> On 10/22/25 10:12 PM, EricT wrote:
> > This works both before and after the feature if adopted, so code can
> > be migrated proactively. The pragma approach would help identify all
> > $() uses that need updating.
>
> So you appear to be confirming that changing the [expr] syntax *will*
> have side effects that require changes in other code.
>
> I'm generally agnostic about language changes to Tcl, and I don't have a
> strong opinion about the various alternatives presented in this
> discussion. I'll leave that to the experts.
>
> However, the cranky, "don't make it worse" developer in me is prompted
> to ask: Why should other parts of my code have to change to accommodate
> this language update that I may not even use?
>
> If the answer is, "We are now in Tcl 9, and breaking changes are OK," my
> response is, "Sure, that was true for 9.0. The breaking changes were
> planned and long communicated."
>
> In other words -  the issue is not really variable substitution in
> itself, but whether the window for breaking changes is still open. I
> thought we were done with that and the window is now closed.
>
> That's more of a question for the TCT as a whole, and I don't have the
> answer. I am inclined to vote against a TIP with breaking changes
> because I don't like breaking changes, but I am open to being persuaded
> on the larger topic - that we are not done making those kinds of changes
> to the language and it's OK.
>
> --Kevin
>
>
>
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