Given the following documented "Bug":

Currently, assigning a boolean value to a variable causes the booleanity to be lost. This code dies:

    $x = true;
    isBoolean($x) || isTrue($x) or die;
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I'm not terribly surprised that such a fundamentally broken module isn't widely used. I've also never found the supposed lack of a boolean data type in Perl to be a problem. I also find the way that isTrue() and isFalse() are defined to look like really bad ideas (because they make the existance of such a fundamental bug not surprising).