# Pastebin TUSlZ1m7
# option 1:
if $foo {
    $*ERR.say: 'foo is true';
    exit 1;
}

# option 2:
{
    CATCH {
        default {
            $*ERR.say: .message;
            exit 1;
        }
    }
    die 'foo is true' if $foo;
}