{
    my ($indent, $depth) = ( "\t", 0 );

    my $_print = sub {
        print $indent x $depth, substr( $_[0], 0, $_[1] );
    };

    my $_call_f1_f2 = sub {
        my $str = shift;

        my ($pos, $first) = f1( $str );
        return ($pos, 0) if !defined $first;

        if ( $first eq CONST1 ) {
            $depth--;
            return ($pos + 1, 0);
        }

        $pos = f2( $str, $first );
        return ($newpos + 2, 0) if defined $pos;

        return ($pos, 1);
    };

    sub pp {
        return unless @_;
        my ($str) = @_;

        my ($pos, $depth_mod) = $_call_f1_f2->( $str );

        $_print->( $str, $pos );

        $depth += $depth_mod;

        $str =~ s[^.{$pos1}\s*][];
        return $str;
    }
}