TCL regsub to variable?

Question

I'm setting up macros, Set, and Say. Defined in procedures.

proc Set {key value args} {
    set ::$key $value
            set "::key2" "$key"
}

proc Say {key} {
puts $key
}

proc Say2 {key} {
set key3 [regsub "\%" $key "\$"]
puts $key3
eval puts $key3
}

Which allows me to execute the following:

Set "test" "this should display this test text"
Say $key2 ;#should display the key "test" which is what we just set
Say $test ;#presents the value of the key test

Output

% Set "test" "this should display this test text"
test
% Say $key2 ;#should display the key "test" which is what we just set
test
% Say $test ;#presents the value of the key test
this should display this test text

So now lets say I want to reassign the variable $ to %

Set "mouse" "squeak" ;#set key mouse with value string of "squeak"
Say $mouse ;#displays the value as set above correctly
Say2 %mouse ;#start using our own characters to represent variables - switch the % for a $ and then output

However I then get when using eval,

 can't read "mouse": no such variable

Output

% Set "mouse" "squeak" ;#set key mouse with value string of "squeak"
mouse
% Say $mouse ;#displays the value as set above correctly
squeak
% Say2 %mouse ;#start using our own characters to represent variables
$mouse
can't read "mouse": no such variable

I'm finding this weird because we set it above, we can recall the value using the standard $ And I can prove that the regsub in Say2 is working as it should replacing % with $.

%mouse becomes $mouse which is a valid variable. Eval $mouse outputs with no such variable

Am I missing something?

Thanks

Answer 1

The issue is with the proc:

proc Say2 {key} {
    set key3 [regsub {%} $key {$}]
    puts $key3
    eval puts $key3 ;# here
}

$mouse does not exist in this proc. It was not passed as a parameter, nor was it created with set. It exists however in the global namespace. One way to reach for it is to use uplevel in this case:

proc Say2 {key} {
    set key3 [regsub {%} $key {$}]
    puts $key3
    uplevel puts $key3
}

Another option I often use is upvar to bring the variable inside (though in this case, we don't want the $ anymore):

proc Say2 {key} {
    set key3 [regsub {%} $key {}]
    puts $key3
    upvar $key3 var
    puts $var
}

_{PS: I also went ahead and removed some backslashes since they aren't really needed in that scenario.}