Perl6 Grammars Keeping State

my $GLOBAL-BINARY = False;
grammar Foo {
    regex TOP {
        :my Bool $*BINARY;
        <ab>+
        { $GLOBAL-BINARY = $*BINARY with $*BINARY }
    }
    token ab { <a>+ (<b>+)? }
    token a  { 'a' {$*BINARY = True} }
    token b  { 'b' {$*BINARY = False} }
}

my $f = Foo.parse('a');
say $GLOBAL-BINARY;
$f = Foo.parse('ab');
say $GLOBAL-BINARY;
$f = Foo.parse('aba');
say $GLOBAL-BINARY;
$f = Foo.parse('abac');
say $GLOBAL-BINARY;
$f = Foo.parse('abbbbbbb');
say $GLOBAL-BINARY;