sub b{unless (!pop) {"unless"} }
sub c{if     (pop)  {"if"    } }
print "failed if (0):         ",c(0), "\n";
print "failed unless (0):     ",b(0), "\n";
print "succeeded if (42):     ",c(42),"\n";
print "succeeded unless (42): ",b(42),"\n";

##</code><code>##

failed if (0):         0
failed unless (0):     1
succeeded if (42):     if
succeeded unless (42): unless