integration failure in perl6

sears-haack integration

sub simpsons(&f, $a, $b, $n) {
    my $h = ($b - $a) / $n;
    my $h2 = $h/2;
    my $sum1 = f($a + $h2);
    my $sum2 = 0;
 
    for $a+$h, *+$h ... $b-$h {
        $sum1 += f($_ + $h2);
        $sum2 += f($_);
    }
    ($h / 6) * (f($a) + f($b) + 4*$sum1 + 2*$sum2);
}


constant R_max = 6.75 / 2;
constant Length = 83;
sub sears-haack($x, $R) { $R * (4*pi*$x*(1-$x))**(3/4) }

say simpsons(&sears-haack.assuming(*, R_max / Length), 0, 1, $_) for <10 100 1000>;