MAIN works

$ cat MAINtest 
sub MAIN($a, $b = 1) {
    say '$a ', $a;
    say '$b ', $b;
}

$ perl6 MAINtest 
Not enough positional parameters passed; got 0 but expected between 1 and 2
in Main (file src/gen_setting.pm, line 324)

$ perl6 MAINtest f
$a f
$b 1

$ perl6 MAINtest f 2
$a f
$b 2