sub outer {
        %trans = _get_transition_table();
        
        my $f = $trans{'start'};
        my $result = 0;
        
        do {
            $result = $f1->();
            my $state = ($result) ? "$f.true" : "$f.false";
            $f = $trans{ $state };
        } while ($f);
        
        return ($result);
    }
    
    sub _get_transition_table {
        my $f1 = \&f1;
        my $f2 = \&f2;
        my $f3 = \&f3;
        [...]
        
        return (
            "start"     =>  $f1,
            "$f1.true"  =>  0,
            "$f1.false" =>  $f2,
            [...]
        );
    }