my $x = 42;
assert '$x > 40';   # assertion fails,
                    # because eval can't see $x

##</code><code>##

sub assert (&) {
   require Carp;
   (shift)->() ? 1 : Carp::croak('Assertion failed')
}

my $x = 42;
assert { $x > 40 };   # assertion ok

##</code><code>##

sub TRUE         () { 1 }
sub FALSE        () { 0 }
sub EXIT_SUCCESS () { TRUE }