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

[Emiliano <emi...@gm...>]

On Tue, 21 Oct 2025 08:02:55 +0000
Zaumseil René via Tcl-Core <tcl...@li...> wrote:

> Hello
> 
> I currently do not see the benefit of this proposal, except some char less to type.
> IMHO expr has some problems or room for enhancements:
> 
>   1.  Double evaluation of arguments
> 
> Could be solved with a new command with only 1 argument
> 
>   1.  Returns only one value
> 
> See p.e. tip 647 syntax

In case you are interested, I wrote a quick POC of tip 647, available at

https://chiselapp.com/user/egavilan/repository/mexpr

Sample usage:

# 1 argument
% package require mexpr
0.1
% ::mexpr::let {
    a {rand()}
    b {3*$a}
    b {sqrt($b)}
}
0.6664191757638097 1.9992575272914292 1.4139510342623005
% list $a $b
0.6664191757638097 1.4139510342623005

# multiple arguments
% ::mexpr::let a {rand()} b {3*$a} b {sqrt($b)}
0.5070870623491178 1.5212611870473536 1.2333941734284923
% list $a $b
0.5070870623491178 1.2333941734284923

# 1 argument, using -local
% unset a b
% ::mexpr::let -local {
    a {rand()}
    b {3*$a}
    b {sqrt($b)}
}
0.20174559122032745 0.6052367736609824 0.7779696482903317
list $a $b
can't read "a": no such variable

# with -local, all referenced variables must be either defined first
# or reached using their qualified name
% set c 4
4
% ::mexpr::let -local b {3 * $c}
can't read "c": no such variable
% ::mexpr::let -local b {3 * $::c}
12

I've left out the magic variable names; all set values are collected
and returned.

Feel free to change and experiment.

Regards

-- 
Emiliano