Reporting system and potentially Python

Yawar Amin yawar.amin at
Fri Jul 8 20:15:14 EDT 2011


On 2011-07-08, at 01:15, Yawar Amin wrote:

> […]
> I like the idea of XML -> HTML + CSS + JavaScript plots. How about moving to a completely declarative XML report, where we use XML tags to ask for things like account names and balances, and using the Scheme (or […]

I got to thinking that Scheme itself can be used as a declarative,* domain-specific language for defining GnuCash reports. We could have a declarative API that sits on top of the currently-existing report API, and abstracts away the complexities of writing out an HTML page and building a report options dialog box. Sort of like LaTeX hides the raw TeX complexities of laying out a page. Here’s my income statement converted over from XML into (declarative) Scheme:

(report "income-statement"
  (def-date "start-date" "General/Start date" "2011-01-01")
  (def-date "end-date" "General/End date" "2011-07-31")

  (def-label "title" "General/Report title" "Income Statement")
  (def-label "subtitle" "General/Report subtitle"
   '((string (date "start-date"))
   (string (date "end-date"))))

  (def-account-group "income" "Accounts/Income accounts"
  (def-account-group "expenses" "Accounts/Expense accounts"
  (def-account "net-profit-loss" ""
   "Net Profit (Loss)"
    (balance (account-group "income"))
    (balance (account-group "expenses")))))

 (title (label "title"))
 (subtitle (label "subtitle"))

 (filter-date (date "start-date") (date "end-date”)
  (group-date 'month
    (account-group "income")
    (account-group "expenses")
    (account "net-profit-loss")))))

And here’s the report structure in plain language:

 definitions (can double as options for the report options dialog box)
  definition of date (start date)
  definition of date (end date)
  definition of label (report title)
  definition of label (report subtitle)
  definition of account group (income)
  definition of account group (expenses)
  definition of a calculated account (net profit or loss = income - expenses)
 report title
 report subtitle
 filter by date (only include transactions within date range)
  group by date (monthly–this should show balances in the table as one column per month)
   tabular display (we could also provide a graphical display–i.e. column chart)
    account group (income)
    account group (expenses)
    account (net profit or loss)

What I’m trying to express here is that a tabular layout should know how to display accounts and groups of accounts: put the account name on the left and the balance on the right. And that the report engine should know how to re-use the definitions of account groups, labels, and dates to build up the options dialog box. We can help it along a little, e.g. in the call to (def-date "start-date" "General/Start date" "2011-01-01") you see that the second argument is a string that provides the tab the widget should be placed in (“General”) and widget’s label for the dialog box (“Start date”), separated by a slash. Oh, and since it’s a def-date, the option widget should be a date picker. This functionality can all be behind the scenes, leaving the report developer to just declare what his/her report should contain.

Note that in the call to (def-account "net-profit-loss" "" Net Profit (Loss)" …) the second argument is an empty string, meaning don’t place this as a widget in the options dialog box.

If we stick with Scheme, we can take advantage of all the low-level functions that already exist for data extraction and report layout. But we can also move to a declarative model where we can have convention (re-use the report definitions as options) over configuration (build an options dialog box).

Also, is it still true that we have to restart GnuCash every time we change a Scheme report, to see the changes? In any case, we need to make it dead easy for users to import and run and custom reports.



* I find that I’m saying ‘declarative’ a lot nowadays–I think it has to do with the fact that I’m learning Haskell :-)

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