To grey out the "cos" button, use 
    $cos->configure(-state => 'disabled');

[download]
with $cos being the Tk::Button object. To be able to enable it again when cos is valid input again, you need to maintain the state of the math input in a variable.

In reply to Re: Perl/Tk question by saintmike
in thread Perl/Tk question by joelnackman

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