sub is_valid { 0 }

is_valid()
   or die "invalid";         # Ok (dies)

my $invalid = is_valid()
   or die "invalid";         # Ok (dies)

my ($invalid) = is_valid()
   or die "invalid";         # XXX (Doesn't die!)

##</code><code>##

%data = (
    foo => !!is_foo(),
    bar => !!is_bar(),
);

##</code><code>##

%data = (
    foo => is_foo(),
    bar => is_bar(),
);