<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
function d($s) {
    if($s == null) {
        throw new Exception("Argument was null");
    }
    return "D";
}

function c($s) {
    return "C" . d($s);
}

function b($s) {
    return "B" . c($s);
}

function a($s) {
    try {
        echo "A" .  b($s);
    } catch(Exception $ex) {
        echo $ex->getMessage();
    }
}

a("x");
a(null);
?>