Custom Reports Using Eguile

What is eguile?

eguile is a way of processing a template file to create a guile script.

More specifically, within GnuCash, guile is used to combine HTML and guile code to create a report, such as an invoice or balance sheet.

The GnuCash version of eguile is eguile-gnc.scm, written in early 2009 by Chris Dennis, and based on Neale Pickett's eguile.scm.

For example,

<h3><?scm:d coyname ?></h3>
<h2><?scm:d reportname ?> as at <?scm:d (gnc-print-date opt-date-tp) ?></h2>

would become

(display "<h3>")(display "Acme Tools Ltd.")(display "</h3>
<h2>)(display "Balance Sheet")(display " as at ")
(display "05/04/2009")(display "<h2">)

which is then evaluated as guile code to create the text of the report.

How to install an eguile report

To try out eguile-based reports, you first need to download eguile-gnc.scm and put it into the report folder. On my system -- Ubuntu -- that's /usr/share/gnucash/guile-modules/gnucash/report/eguile-gnc.scm. In general, it should go into the same folder as files such as fancy-invoice.scm.

Note: GnuCash 2.3/2.4 already includes eguile-gnc.scm.

Install the report and its associated files in the usual way (see Custom Reports#Loading the Report for a full explanation).

Your report should start with a define-module statement like

(define-module (gnucash report my-report-name))

and have a unique name (GnuCash 2.2.x and before)/a unique id (GnuCash 2.3.x and later).

The easiest way is to put all the files for a report into your .gnucash folder, and then add a line to .gnucash/config.user like this:

(load "/path/to/my/.gnucash/report.scm")  

If .gnucash/config.user does not already exist, just create it and add the new line.

For example, on a Linux system, for a user called 'chris', the Tax Invoice report can be installed by:

1. Downloading taxinvoice.scm and taxinvoice.eguile.scm, and putting them into the /home/chris/.gnucash/ folder.
2. Adding this line to /home/chris/.gnucash/config.user:

(load "/home/chris/.gnucash/taxinvoice.scm")

Restart GnuCash, and the report should then show up somewhere in the reports menu, depending on the menu-path option in the report. The Tax Invoice and Balance Sheet reports (see below) put themselves into the Reports/Business sub-menu.

How to create an eguile report

...

eguile syntax

Within what is otherwise an HTML source file, Guile/Scheme code is wrapped in '<?scm ... ?>' (whitespace is required after '<?scm' and before '?>')

'<?scm ... ?>' pairs can NOT be nested.

The optional :d modifier (i.e. '<?scm:d' ) is just a shortcut for '(display ... )', so '<?scm:d x ?>' is the same as '<?scm (display x) ?>'

Note that s-expressions can be spread across more than one '<?scm ... ?>', for example:

<?scm (if (> x 3) (begin ?>Bigger<?scm ) (begin ?>Smaller<?scm )) ?>

Each chunk of text outside a '<?scm ... ?>' pair ends up wrapped in a (display ... ), after having had double quotes etc. escaped.

The processing happens in two passes. Initially the input file is converted to a Guile script, and then that script is evaluated to produce the final result (as a string which is passed back to the report-displaying part of GnuCash).

For example, if the input file contained these lines:

 <h1 align="center">Invoice <?scm:d invoiceid ?></h1>
 <?scm (for entry in entries do ?>
   <p>Date: <?scm:d (entry date) ?>, description: <?scm:d (entry desc) ?>
 <?scm ) ?>

the resulting script would look like:

 (display "<h1 align=\"center\">Invoice ")(display invoiceid)(display "</h1>")
 (for entry in entries do
   (display "<p>Date: ")(display (entry date))
   (display ", description: ")(display (entry desc))
 )

and the final result might be this:

 <h1 align="center">Invoice 002345</h1>
   <p>Date: 04/03/2009, description: Widgets
   <p>Date: 05/03/2009, description: Modified widgets

...

Custom for-loop syntax

To simply looping over a list or map (which by default is a bit cumbersome in scheme), GnuCash defines a custom for-loop syntax, which works similar to for loops in some imperative languages. There are three forms of this syntax: For a single list, for multiple lists and for hashes. This for loop syntax should be available in all eguile-based reports (both in the report itself as well as in the eguile templates). This syntax is defined in eguile-utilities.scm, so it might be available in other parts of scheme as well.

Single list

(for <var> in <list> do <expr> ...)

This syntax loops over <list>, assigning each value to <var> in turn and evaluating all <expr>'s. In other words, it takes the first element of <list>, assigns it to <var>, evaluates each <expr>, takes the second element of <list>, etc.

Consider the following example:

(for entry in (gncInvoiceGetEntries invoice) do
  (displayEntry entry))

This example would evaluate the "displayEntry" function for each entry in a given invoice.

Multiple lists

(for (<var> ...) in (<list> ...) do <expr> ...)

This syntax loops over all <list>'s in parallel, assigning each value to the corresponding <var> and evaluates all <expr>'s. In other words, it takes the first element of the first <list>, assigns it to the first <var>, takes the first element of the second <list>, assigns it to the second <var>, up to the last <list> and <var>. Then it evaluates each <expr> and starts over with the second element of each list, etc.

Consider the following example:

(let ((descriptions (list "Company name" "Address" "Website"))
      (values (list "Example Corp" "Example street 1" "http://example.org")))
  (for (desc val) in (descriptions values) do
    (display desc)
    (display ": ")
    (display val)
    (display "<br/>\n")))

This example would output:

Website: http://example.org<br/>
Company name: Example Corp<br/>
Address: Example street 1<br/>

Hashes

(for <key> => <value> in <hash> do <expr> ...)

This syntax loops over all keys and values in a hash, assiging each key to <key> and each value to <value> in turn and evaluating all <expr>'s. Note that as always with hashes, the keys from the hash are looped in arbitrary order.

Consider the following example:

(let ((company (make-hash-table 16)))
  (hash-set! company "Company name" "Example Corp")
  (hash-set! company "Address" "Example street 1")
  (hash-set! company "Website" "http://example.org")
  (for desc => val in company do
    (display desc)
    (display ": ")
    (display val)
    (display "<br/>\n")))

This example would output exactly the same as the previous example.

Internationalisation

Always use _ rather than N_ in the template file. N_ can be used for report option names, help text, and default values.

More precise N_ means NOP, no operation. It can be used to mark strings for translation e.g. in array declarations, but doesn't translate them. Then later the translation is called with _. More Details in Translation#Tips for Developers.

Available Reports

The following eguile-based reports are available. More will be contributed soon (hopefully).

Tax Invoice

Report file:	taxinvoice.scm
Template file:	taxinvoice.eguile.scm
CSS file:	none
Sample output:	PDF
Author:	ChrisDennis
Version:	0.01
Last update:	June 2009

Features

• Includes full company and customer details, including a company logo if required.
• Automatically includes only relevant columns. For example, if none of the items on the invoice have discounts applied, then the discount columns will be omitted.

Issues

• taxinvoice.scm includes code to display individual taxes on a per-entry basis, i.e. on each line of the invoice. This relies on a fix to the Swig encoding that is currently in the pipeline as bug #573645, but it includes a work-around so that it simply misses out the extra columns if that fix hasn't been applied. This bug has been fixed in 2.3/2.4.
• Doesn't have a separate CSS file (yet).

Balance Sheet

Report file:	balsheet-eg.scm
Template file:	balsheet-eg.eguile.scm
CSS file:	balsheet-eg.css
Sample output:	PDF
Author:	ChrisDennis
Version:	0.01
Last update:	June 2009

Features

• Displays the balance sheet in a 'text book' style with rules under columns etc.
• Uses the 'Assets = Equity + Liabilities' model. If there is demand for an 'Assets - Liabilities = Equity' version, then that could be done as a separate report, or by adding an option and some extra code to this one.
• One- or two-column layout.
• Negative values can be shown as, for example, '-£100.00' or '(£100.00)'.
• Deliberately has fewer options than the standard balance sheet. It makes 'intelligent' decisions about what to display. For example, parent accounts that are marked as placeholders and have a zero balance do not have their balance shown at all.
• Handles commodities/currencies in a basic way -- exchange rates are calculated as at the date of the balance sheet.
• A balancing entry (labelled 'Retained Earnings' by default) is calculated so that the sheet always balances.
• Only displays Imbalance and Orphan accounts if non-zero.
• Does not have a account selection option -- I don't see why you would want a balance sheet with some accounts missing.
• Does not deal with unrealised gains/losses.

To Do

• Option to put the currency symbol at the top of each column, rather than on every value.
• Option to put "Less: " in front of negative accounts, e.g.

 Less: Drawings        (£1000.00)

Issues

• Needs people to test it and comment on it.