{   package Stream;
    use Moo;

    has fh => (is => 'ro');
    has _buffer => (is => 'rw', default => "");

    sub next_token {
        my ($self) = @_;
        my $buffer = $self->_buffer;
        until ($buffer =~ /\S/) {
            $buffer = readline $self->fh;
            die "End of file" unless defined $buffer;
        }
        $buffer =~ s/(\S+)//;
        my $token = "$1";
        $self->_buffer($buffer);
        return $token
    }
}