my $flipflop = 0;

sub foo {
    use Want qw(want);

    print 'not ' if !want 'BOOL';
    print "bool\n";

    return $flipflop=!$flipflop;   # alternate true and false
}

for (1..3) {
    while (foo() ) {
        # print "here 1\n";
    }
    while ($answer = foo() ) {
        # print "here 2\n";
    }
}