I don't use Tk and therefore i didn't really read the friendly manual
This is not Tk related. This is referencing in Perl.
that the construct hotchiwawa mentions can be found here and here
No, it can't. There's a big difference between the two: 
my $value_ref = \&callback();
my $code_ref  = \&callback;   # <-- See? No parentheses!

[download]
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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In reply to Re^4: Can't get Dialog or messageBox to work from button by choroba
in thread Can't get Dialog or messageBox to work from button by SwaJime

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