[GNUe-dev] AppServer - list datatype

[kilo]

Hello folks

Playing with invoicing I decided to store only the net value
of a product and it's VAT percentage. Given these two datae I can
compute the VAT value and the gross value of an invoice item. These
computations are done by calculated fields in the invoice.gcd. There are
3 procedures also, that make up the totals of net, VAT, gross values of
invoice lines. When displaying all these information about an invoice
(with several lines, or better, items), the following calls are done:   
getTotalNet        Item1.getNet
        Item2.getNet
        ...
        ItemX.getNet
        return sum(net values)

    getTotalVat
        Item1.getVAT
            Product1.getVatPercent
            Item1.getNet
            compute vatValue1
            return vatValue1
        Item2.getVAT
            Product2.getVatPercent
            Item2.getNet
            compute vatValue2
            return vatValue2
        ...
        ItemX.getVAT
            ProductX.getVatPercent
            ItemX.getNet
            compute vatValueX
            return vatValueX
        return sum(VAT values)

    getTotalGross
        Item1.getGross
            Item1.getNet
            Item1.getVAT
                Product1.getVatPercent
                Item1.getNet
                compute vatValue1
                return vatValue1
            compute gross value1
            return gross value1
        Item1.getGross
            Item2.getNet
            Item2.getVAT
                Product2.getVatPercent
                Item2.getNet
                compute vatValue2
                return vatValue2
            compute gross value2
            return gross value2
        ...
        ItemX.getGross
            ItemX.getNet
            ItemX.getVAT
                ProductX.getVatPercent
                ItemX.getNet
                compute vatValueX
                return vatValueX
            compute gross valueX
            return gross valueX
        return sum(gross values)


If I could implement procedures, that return 3 values I am interested
in, the above procedure could become much simpler:    getTotals
        list1 = Item1.getValues
            Product1.getVatPercent
            Item1.getNet
            compute vatValue and gross
            return net, vatValue, gross as list
        list2 = Item2.getValues
            Product2.getVatPercent
            Item2.getNet
            compute vatValue and gross
            return net, vatValue, gross as list
        ...
        listX = ItemX.getValues
            ProductX.getVatPercent
            ItemX.getNet
            compute vatValue and gross
            return net, vatValue, gross as list

        and here I could sum up the net, vat and gross values stored in
the lists. Or tuples.

As it can be seen on the above example, it would become much more
efficient if procedures could return lists or tuples or dictionaries.

Of course the above example is an example only. It could be solved with
redundant data stored in the DB - which in reality should be done that
way for other reasons also. So it is only an example.

kilo
Kmetykó Gábor