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bool is_bool ( mixed $var )

<?php
$a = false;
$b = 0;

// Since $a is a boolean, the result is true
if (is_bool($a)) {
    print "Variable a is a boolean";
}

// Since $b is not a boolean, the result is false
if (is_bool($b)) {
    print "Variable b is a boolean";
}
?>

Variable a is a boolean