package Series;

use strict;

sub TIEARRAY {

    my $pkg = shift;

    my $rsub = shift; # sub for formula

    my @vals = @_;

    bless { 'values' => [ @vals ],
            'next' => $rsub
            }, $pkg;

}

sub FETCHSIZE {

    # rather meaningless in context, but gets called a lot
    # presume it's to check that any values at all exist

    return 1; # for now
}

sub FETCH {

    die "can't get subscripted value of series";

}

sub SHIFT {

    my ($obj) = @_;

    my $ra = $obj->{'values'};

    push(@$ra, $obj->{'next'}->(@$ra));

    return shift @$ra;
}

1;