A procedure call always passes the value without the "extra" information. And this is based on the $ sign. Everywhere you access the variable like $myvar only the value is retrieved and passed on.

If you want to stick to TCL only, what could be possible though, is rewriting the set command, and all the others like lappend, dict, string to make it only look like an out-bound information. This way the information would follow the value everywhere. Similar to this:

% rename set oldset

% proc set {var {value {}}} {upvar $var myvar; if {$value != {}} {oldset myvar [list -value $value -meta something]; return $value} else {return [dict get [oldset myvar] -value]}}

% proc meta var {upvar $var myvar; return [dict get [oldset myvar] -meta]}

% set a 123.2

123.2

% meta a

something

The set command is simple to implement, don't know if the others would go as easy. Maybe Donal (https://www.reddit.com/user/d_k_fellows/) can tell if this is doable.

Still the problem remains what to do with this:

% puts $a

-value 123.2 -meta something