Re: [TCLCORE] Prototype Implementation of TIP 672 - $(expr) Syntax

[Kevin K. <kev...@gm...>]

On Mon, Oct 20, 2025 at 7:22 PM EricT <tw...@gm...> wrote:

> You're right that {=}{expression} avoids this particular incompatibility. I think {=} could potentially work, though my sense is it would require more extensive parser changes to handle quotes and bare words (where $ already works naturally). But I could be wrong about the implementation complexity.
>
>
The parser changes are pretty minimal, and nearly parallel to the
implementation of {*}. The {=} would be presumed to be followed by a
'word', with all the usual rules that implies.

{=}{$a + $b} would be parsed by the ordinary balancing of curly braces,
followed by processing the content as an expression.

{=}[command], {=}"quoted string", {=}$var, etc, would all have natural
meanings equivalent to applying [expr] to the substituted value.
(Ordinarily, those uses should be advised against, since all these forms
ask for double substitution and invite code injection attacks, but I can
see them having their place in some specialized contexts, and the syntax is
thereby rendered uniform.)

(I'd actually favor {$} over {=}, and instead reserve {=} for the
possibility of a new 'little language' for less cumbersome expressions (in
particular, automatic $-substitution of barewords, and implementation of =
for assignment. But that's a different idea altogether, and has had several
rejected or abandoned TIPs over the years.)

-- 
73 de ke9tv/2, Kevin