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issue 21: blurb about the March 2011 meeting

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1((title . "Issue 21")
2 (authors "Andy Bennett")
3 (date . 1321465864))
5== 0. Introduction
7Welcome to the 21st issue of the Chicken Gazette. While the gazette
8was on hiatus the chicken community was definitely not.
10With the stabilisation of Chicken 4.7 well underway since the last
13Some people have also started to set up salmonella farms and C-Keen
14has completed his "Chicken Zoo".
19== 1. Chickens Out & About
21=== Nuremberg (December 2011)
22[[|Christian Kellermann]] wrote
23([[|2011/10/22 17:38Z]]) to
24confirm the planned Chicken Hacking Sprint scheduled for the beginning of December.
26Interested and available Chickenauts will meet in Nuremberg on the weekend of 9th, 10th and 11th
27of December. If you haven't done so already, you can let us know that you will be joining us by
28placing a note at the foot of the [[|wiki page]].
29If you can't attend in person then we'll be keeping an eye on IRC so feel free to book yourself
30a slot in your cave at home and join us throughout the weekend and into the evenings, Central European Time.
32For those of you keeping score, this will bring the total number of Chicken meets this year to
335 (FOSDEM, Cologne, FrOSCon, T-DOSE and Nuremberg).
36=== Cologne (March 2011)
38In March, Chickens met up at the Chaos Computer Club in Cologne, Germany for a Chicken Hacking Weekend. Here's
39[[|Moritz Heidkamp]]'s report on what they got up to.
41The usual suspects [[user:peter-bex|Peter Bex]],
42[[user:felix-winkelmann|Felix Winkelmann]],
43[[user:christian-kellermann|Christian Kellermann]] and me met for two
44and a half days of exchanging ideas and hacking. While we also fixed a
45good share of bugs our main goal for this weekend was to create a
46working prototype of a distributed egg system. By the end of Sunday,
47mostly thanks to Peter's effort, we had something that was already
48pretty similar to what is in use today (see
49[[|his announcement on the mailing list]]). Apart
50from that some interested visitors stopped by every now and then. Some
51nice chats, food and the occasional beers were had which hopefully
52helped to spread the Chicken word.
55=== FrOSCon (August 2011)
56At FrOSCon in August we sported not only a project booth but a presentation room as well so we took the
57opportunity to lay on a couple of talks for the delegates.
59[[|Moritz Heidkamp]] presented
60"[[|An introduction to Lisp]]:
61Why to talk to computers in parentheses" whilst
62[[|Christian Kellermann]] offered
63"[[|A guided tour through the republic of CHICKEN]]:
64get up to speed with the practical scheme implementation".
65[[|Christian]] has been keeping his talk up-to-date and
66you can find the latest version [[|on the wiki]].
68Naturally, there are [[|pictures]].
71=== T-DOSE 2011 (November 2011)
72European Chickens met up at T-DOSE in Eindhoven, The Netherlands on the weekend of the 5th, 6th and 7th of
73November. [[|Peter Bex]] arranged for us to contribute a "Chicken
74Scheme Project Booth" and we subsequently lured a few Dutch hackers into #chicken on IRC.
76[[|Christian Kellermann]] knocked up some impressive demos
77of [[|PONG]] using Chicken's [[|Cairo Egg]].
79[[|Alaric Snell-Pym]] finished off the tests for his
80[[|Ugarit]] backup egg which allowed him to release version 1.0.
82...and [[|Moritz Heidkamp]] started on a replacement for the
83[[|Environments Egg]] as it has unfortunately has been overtaken
84by developments in the Chicken development branch.
86Pictures are up in the [[|usual place]] on the Chicken website.
90== 2. Chicken Talk
92=== R7RS to be dedicated to the memory of John McCarthy
94Matt Welland wrote in with the sad news that the "Father of Lisp", John McCarthy had sadly passed away ([[|2011/10/25 15:59Z]]). [[|John Cowan]], member of the R7RS working group, told us that R7RS,
95the upcoming version of the Scheme standard, would be dedicated to his memory ([[|16:22Z]])
98=== Parallel build patch for Chicken Makefile
100A lively discussion broke out on the [[|Chicken Users mailing list]] regarding
101[[|parallelisation of the Chicken build process]].
103Vitaly Magerya supplied a [[|patch]] (2011/10/06 12:37Z) to fix some problems
104he'd been having with builds failing when specifying the {{-j}} to {{gmake}}.
105[[|Mario Domenech Goulart]] noted that this functionality was already being
106addressed by [[|ticket 526]]
107([[|2011/10/06 12:39Z]]) and Vitaly was keen to see it committed
108soonly as he maintains the FreeBSD port and people had been asking him for parallel builds ([[|2011/10/06 14:24Z]]). Whilst still keen, [[|Mario]] [[|advised caution]] as he wanted to see it proven ([[|2011/10/06 14:40Z]]).
110Vitaly was keen to push things forward ([[|2011/10/06 15:45Z]]) and
111offered continued testing under FreeBSD 8.2-RELEASE on x86_64. He noted that, as far as he could tell, {{gmake check}} passed when using his
112patch, modified with [[|Moritz Wilhelmy's suggestions]]. Moreover, he
113offered to try the patch from [[|ticket 526]] as well.
115[[|Mario]] [[|suggested]]
116that using the [[|ticket 526]] patch was a good idea as it had, as far as he knew, received testing under Linux and MacOSX.
118Toby Thain spoke in favour of the patch, saying that a working parallel build gives confidence that the Makefile is, in fact, correct.
119He offered to test on three platforms, namely Solaris 10 SPARC SMP and both PowerPC and Intel version of MacOSX SMP.
121Vitaly updated the [[|ticket 526]] patch to the then current sources and confirmed that the build worked at {{-j8}}
122and the tests passed in his FreeBSD 8.2-RELEASE, x86_64 environment. He did, however, note that parallelisation does not work for the install phase
123([[|2011/10/08 12:29Z]]).
125Toby Thain reported successful builds on the 64-bit version MacOSX-10.6 as well as MacOSX-10.5 on a dual-processor G5. He noted "{{make -j8}}
126reduces the make step from 3:39 to 0:47 on my 8-core system". Unfortunately {{make check}} did not pass on either system, with or without the patch
127([[|2011/10/12 01:59Z]] &
128[[|2011/10/15 19:53Z]])
130[[|Christian Kellermann]] noted that it might necessary to install the compiled binaries
131([[|2011/10/15 20:07Z]]) however, Toby did not report back as to whether this
132had any effect on the results of the tests.
135=== 64-bit SPARC Build
137Nicolas Pelletier came to the [[|mailing list]]
138unable to build for Solaris 10 running on SPARC64 due to a missing {{apply-hack.S}}
139([[|2011/11/09 11:48Z]]).
141It turned out that there was no SPARC64 support for Chicken at all and [[|John Cowan]]
142came to the rescue ([[|15:36Z]])
143with instructions for how to add it to the supported architectures list and disable the
144apply hack. [[|Christian Kellermann]] chimed in with affirmations
145around the utility of using Chicken without an apply hack ([[|15:54Z]])
147Nicolas struggled with disabling the apply hack ([[|2011/11/10 11:10Z]])
148due to the Two Lies Of The README. Over the course of the next few minutes [[|Christian]]
149and [[|Mario Domenech Goulart]]]
150confirmed that the lies, which related to the way bootstrap compilers are distributed and invoked, had
151already been fixed in the development versions.
153Meanwhile, Toby Thain tried the build on his SPARC64 ([[|12:40Z]])
154and discovered that GNU make 3.82 is required as well as the addition of {{-lrt}} in {{Makefile.solaris}}. Toby's
155build eventually succeeded and appeared to be good, albeit having only used 1 of his 4 CPUs and with a couple of {{make check}} errors.
157Later on the Thursday, [[|Jim Ursetto]] noted ([[|16:47Z]])
158that the [[|parallel build patch]] in
159[[|ticket 526]] still works on Chicken Toby [[|confirmed]]
160that the patch did indeed work on Solaris and build time was reduced to 10 just of his Earth minutes from the original 40.
161Of course, user time across the four CPUs was still in the region of 40 minutes in total. :-)
163To round everything off, Toby offered [[|binary SYSV packages for Solaris 10 on SPARC64]].
164Contact him via the [[|mailing list]] if you're interested.
167=== Static Linking & Standalone Binaries.
169Serg Kozhemyakin [[|asked]] whether it is possible to build static
170binaries after having trouble using the {{-static}} flag to {{csc}}. He also wondered about building standalone binaries for Windows.
171[[|Christian Kellermann]] [[|advised]]
172against static linking as many of the eggs cannot cope with it. He did, however, suggest that the {{-deploy}} option may well solve both
173issues as it ensures that all the DLLs (including the Chicken runtime and other shared objects) are bundled together into a single directory.
176=== Tracing with {{,tr}} moved to an egg
178[[|Mario Domenech Goulart]] [[|helped]]
179Curtis Cooley in his [[|search for the {{,tr}} command]].
180The functionality had been moved from the core into an egg in Chicken 4.3.0.
183=== {{gmake check}} sometimes fails.
185Pekka Niiranen wrote to tell us about
186[[|problems with {{gmake check}} in Chicken 4.7.0-st]]
187on OpenBSD 5.0.
189[[|Jim Ursetto]] [[|said]]
190that one of the failures had been fixed in the stability branch after the Chicken 4.7.0-st release and he filed
191[[|ticket 724]] for the segmentation fault issue.
193[[|Peter Bex]] mentioned that the [[|ticket 724]] segmentation
194fault had also been observed under NetBSD and Arch Linux. He said that "It's known to be broken" but that it is not properly reproducible
195as it only happens some of the time ([[|2011/11/06 09:51|]]).
198== 3. Salmonella and other tests
199Salmonella is Chicken's egg testing framework.
201For some time we have had daily salmonella runs of the master development
202version of Chicken under Linux on x86. Throughout November, MacOSX-x86_64 has also
203been regularly experiencing the runs. [[|Mario Domenech Goulart]] who maintains the testing
204effort at [[]], as well as the [[|Salmonella codebase]]
205itself, is always on the lookout for more feeds. We are aware that testing on
206other platforms is being organised but if you've got a private Salmonella
207running regularly on an interesting operating system or version of Chicken then
208give us a shout and we'll see if we can get it included with the other reports
209on [[]]
211There is also [[|an entirely new version of Salmonella]] over at github so test that too. The new version is more modular -- some features that were previously built in salmonella are now independent eggs (e.g., [[|salmonella-html-report]] and [[|salmonella-feeds]].  There's also a new egg that provides a new feature: [[|salmonella-diff]] which generates HTML output to render differences between two salmonella logs.
213Here's short list of new salmonella features:
215* egg lint mode: salmonella can now easily check for common egg mistakes before the code hits the egg repository.  Just run {{salmonella --this-egg}} from the egg directory
216* a new execution mode that can significantly reduce salmonella execution times.  In this mode, salmonella won't set the temporary egg installation directory empty before installing new eggs.  While this mode won't spot egg dependencies problems, it can drastically effect the execution time
217* a new tool to take advantage of multi-core systems ({{salmonella-epidemy}})
218* a simple text mode log file viewer ({{salmonella-log-viewer}})
219* [[|salmonella-html-report]] generates reverse dependencies graphs.  That can be useful, for
220example, to ilustrate how many eggs depend on a given egg.
223[[|Alaric Snell-Pym]] is one of the people who has been setting up a Chicken testing
224environment. After [[|some discussion]], he chose Chicken 4.5.0 under
225NetBSD ([[|2011/10/06 21:18Z]]). He's been keeping track of all the
226Egg dependencies and plans to publish them as a list of NetBSD pkgsrc packages.
228Thanks to [[|bevuta IT GmbH]], the CHICKEN test
229infrastructure will soon have more machines available to test the
230CHICKEN compiler, tools and eggs.  A new salmonella environment for
231Linux/x86-64 is currently being set up.
233In addition to salmonella, work on the
234[[|Chicken Playground]] project has
235been resumed.  The Chicken Playground project provides environments
236that can be used by tools like {{chroot}} to test CHICKEN tools and
237eggs.  Those environments contain tools and libraries required to
238build and test most eggs.  Currently a Linux/x86 environment is
239available. A Linux/x86-64 environment is under development and should
240be available soon.
242The new test infrastructure, based on new versions of salmonella and
243Chicken Playground and running on new platforms will probably go into
244production during the Nuremberg hackaton.
247== 4. Core Development
251I need some blurb on this from people Who Know.
252I'd like something on the scrutinizer and stability work that's been going on as well as the proposal to bug fix until r7rs
253and then do Chicken 5.0.
258mario, felix, ckeen
259lots of bug fixes, sparc64 support, scrutinizer fixes
261 * On origin/master:
262   * (e1a5437): when conditional branches differ in the number of results, do not merge the results (felix, 2 days ago)
263   * (bae7d92): clustering optimization added (felix, 5 weeks ago)
264   * (b1907c5): use different default stack-sizes on 32/64 bit platforms (felix, 6 days ago)
265   * (986bd3f): disable apply-hack on sparc64 (felix, 6 days ago)
266   * (28a36bf): Remove scripts/make-egg-rss-feed.scm (imported into the chicken-infrastructure repo) (Mario Domenech Goulart, 5 days ago)
267   * (fbeffd1): scripts/tools.scm: needs regex for `string-match' (Mario Domenech Goulart, 5 days ago)
268   * (1fca9c6): use equal? in case MSYSTEM is not defined (makedist.scm) (felix, 6 days ago)
269   * (42a8263): don't remove build-info files on make confclean or it is not possible to build from a tarball without preinstalled chicken (felix, 9 days ago)
270   * (3bb9645): write debugging output for optimizations into generated source file (felix, 3 weeks ago)
271   * (e7fe2fb): allow procedure in operator-position of evaluated list (#705, suggested by John Cowan) (felix, 2 weeks ago)
272   * (e2fb31c): fix subtype check for fixed-size list/vector types in scrutinizer (felix, 10 days ago)
273   * (fd018df): strip std-envs of non-std identifiers, ignore ##sys#macro-environment when evaluating with an explicit environment (felix, 13 days ago)
274   * (fe8f63c): minor change in port-tests.scm to handle case when HOME is not defined (Windows) (felix, 2 weeks ago)
275   * (723a469): cut of union types above a certain length (felix, 2 weeks ago)
276   * (919a7c7): fixes in build + Windows test script, added note to README (thanks to mario) (felix, 2 weeks ago)
277   * (ddb96f9): Also added runtests.bat to manifest. (felix, 3 weeks ago)
278   * (0df9bb8): another trivial fix for making boot-chicken work on cmd.exe (felix, 3 weeks ago)
279   * (cea668f): trivial Windows-related corrections in rules.make, found by Mario - not yet working, though (felix, 3 weeks ago)
280   * (1bc311d): undocumented scrutinize declaration (obsolete), reported by ckeen (felix, 3 weeks ago)
281   * (10494f6): fixed stupid paren-matching error (felix, 3 weeks ago)
282   * (f9a6702): disable debug output in scrutinizer (felix, 5 weeks ago)
283   * (2483f8d): check not necessary for lambda and  warn if using keyword as variable in binding form (felix, 3 weeks ago)
284   * (aa6b2bb): cleaning up uninitialized variables in C_reclaim, add debug output to C_mutate on m-stack resize, grow m-stack at higher rate (felix, 3 weeks ago)
285   * (1e04156): use write-string port-class method (felix, 3 weeks ago)
286   * (59cdaaf): remove obsolete C_h_... allocation functions (pointed out by Joerg Wittenberger) (felix, 3 weeks ago)
287   * (159611d): handle macro-aliases when resolving declared identifier, making sure things are done right inside modules. (felix, 4 weeks ago)
288   * (0cc88a4): removed obsolete file (felix, 4 weeks ago)
289   * (1f56f3a): ##core#type makes subtype-check optional; quit compile when type-mismatches in strict mode (felix, 5 weeks ago)
292== 5. Stability is for Chickens
294[[|Jim Ursetto]] has set up a Chicken Stability Branch
295effort over at [[]]. Jim describes it as "a fork of the Chicken
296Scheme core which backports certain useful bugfixes and minor features from the future to 'stable'
297maintenance versions". Releases for stability/4.7.0 have version numbers like {{4.7.0.x-st}} (for
298example, {{}}). If you're interested in running a stable Chicken in production, we recommend
299that you check out Jim's work.
303== 6. Hatching Farm
305There has been a lot of egg activity over the course of the past few months. I've selected a few,
306focussing on ones that were announced or discussed on the [[|mailing list]].
308TODO: Write about the distributed egg repository
310By far the most notable thing to have happened is the announcment and implementation of the new
311Egg management system.
313* [[|Ivan Raikov]]'s [[|proposal]]
314  to recategorise eggs filed under "Uncategorized or invalid" and "Miscellaneous" was met with enthusiasm with a number of people pitching in to
315  help as well as [[|Peter Bex]] suggesting that the category list be revisited
316  ([[|2011/10/11 08:12Z]]). [[|Peter]]
317  specifically suggested the addition of a "Communication"s category.
319* [[|Thomas Chust]] announced some new eggs: [[|bindings to WebKitGTK+ and JavaScriptCore]], [[|webgate: a tiny (S)CGI application framework]] and a [[|small binding for the BerkelyDB library]]
321* [[|Christian Kellermann]]
322  [[|fixed some bugs]] in the
323  [[|Cairo Egg]] and tagged version 0.1.11.
325* [[|Alan Post]] [[|patched]] the
326  [[|Sandbox Egg]] to bring it up-to-date with API changes in the Chicken core. His patch was duly accepted.
330== 7. Donations
332It's now possible to donate to your favourite scheme (as long as it's Chicken)!
336We've already had two donations since the account opened a month ago so get donating before it fills up! :-)
338Thank you [[|Sven Hartrumpf]] and Ross Lonstein!
341== 8. Omelette Recipes
343This issue's omelette is the second installment of
344[[|Alaric Snell-Pym]]'s
345"financial book-keeping in scheme" series. If you missed the first part,
346check it out [[|here]].
348Now, to make things easy, I parse the ledger by just defining a heap
349of procedures and macros, and then diving into the ledger with
350eval. It's just Scheme code that, as it is executed, builds up the
351data structures. We'll need some helpers to set up third parties
355(define (define-third-party name address group)
356        (let* ((balance-account
357                (make-account
358                 (string-append name ".balance")
359                 'balance
360                 group
361                 #f))
362               (expenses-account
363                (make-account
364                 (string-append name ".expenses")
365                 'delta
366                 'expenses-reclaimed
367                 #f))
368               (third-party
369                (make-third-party
370                 name address balance-account expenses-account)))
371          (account-third-party-set! balance-account third-party)
372          (account-third-party-set! expenses-account third-party)
373          (register-account! balance-account)
374          (register-account! expenses-account)
375          (set! (hash-table-ref *third-parties* name) third-party)))
378Now we can work on a way of representing bills and invoices. A nice
379input syntax would be:
382(define-third-party "clients.widgetcorp" "123 Any Street" 'clients)
383(register-account! (make-account "" 'delta 'income #f))
384(register-account! (make-account "" 'delta 'travel #f))
385(register-account! (make-account "stock.balance" 'balance 'stock #f))
386(register-account! (make-account "cash" 'balance 'cash #f))
387(register-account! (make-account "taxes.vat" 'balance 'vat #f))
389(invoice "INV005" "clients.widgetcorp" (ymd 2011 04 25)
390         (service "" 800 (vat20) "Router setup and installation")
391         (sale "stock.balance" 350 (vat20) "1 of LX300 router, serial number 0343248")
392         (expense (ymd 2011 03 02) "" "cash" 35 () "Travel to site"))
395The idea is that the sales taxes incurred on a line are specified as a
396list after the amount. If there's no taxes due, then we use an empty
397list. Otherwise we have a list of taxes, which are either plain tax
398names (to have the system compute the tax due itself) or two-element
399lists joining a tax name to a precomputed amount (often, when we pass
400on an expense, we know the tax we paid as it's on the receipt, so we
401should use that (even if they made a mistake working it out) rather
402than calculating our own).
404A nice way to implement that might be to make "invoice" a macro that
405absorbs its first three arguments as an invoice code, the name of the
406third party to invoice, and the date; then treats the rest as a body
407to be wrapped in a dynamic environment in which a parameter allows
408{{sale}}, {{expense}}, and {{service}} to add lines to the
409invoice. This is easily arranged:
412(define-record date year month day)
414(define-record invoice
415  name date third-party lines)
417(define (register-line! invoice line)
418  (invoice-lines-set! invoice
419                      (cons line (invoice-lines invoice))))
421;; Compute sales taxes
422(define (compute-tax tax amount)
423  (case tax
424    ((vat20) (* 0.20 amount)) ;; Current UK rate
425    ((vat15) (* 0.15 amount)) ;; Previous UK rate
426    ((vat175) (* 0.175 amount)))) ;; Previous UK rate
428;; Expand a list of taxes, some of which might be bare symbols
429;; naming taxes to work out, or (<tax> <amount>) lists for
430;; ready-computed taxes, into an alist of tax names to tax amounts
431(define (resolve-taxes amount taxes)
432  (map (lambda (tax-desc)
433         (if (list? tax-desc)
434             (cons (car tax-desc) (cadr tax-desc))
435             (cons tax-desc (compute-tax tax-desc amount))))
436       taxes))
438(define-record invoice-service-line
439  income-account amount taxes description)
441(define-syntax service
442  (syntax-rules ()
443    ((service income-account amount taxes description)
444     (register-service! (*current-invoice*) income-account amount 'taxes description))))
446(define (register-service! invoice income-account amount taxes description)
447  (let ((service
448         (make-invoice-service-line
449          (find-account income-account)
450          amount
451          (resolve-taxes amount taxes)
452          description)))
453    (register-line! invoice service)))
455(define-record invoice-sale-line
456  stock-account amount taxes description)
458(define (register-sale! invoice stock-account amount taxes description)
459  (let ((sale
460         (make-invoice-sale-line
461          (find-account stock-account)
462          amount
463          (resolve-taxes amount taxes)
464          description)))
465    (register-line! invoice sale)))
467(define-syntax sale
468  (syntax-rules ()
469    ((sale stock-account amount taxes description)
470     (register-sale! (*current-invoice*) stock-account amount 'taxes description))))
472(define-record invoice-expense-line
473  expense-account payment-account amount taxes description)
475(define (register-expense! invoice date expense-account payment-account amount taxes description)
476  (let ((expense
477         (make-invoice-expense-line
478          (find-account expense-account)
479          (find-account payment-account)
480          amount
481          (resolve-taxes amount taxes)
482          description)))
483    (register-line! invoice expense)))
485(define-syntax expense
486  (syntax-rules ()
487    ((expense (ymd year month day) expense-account payment-account amount taxes description)
488     (register-expense!
489      (*current-invoice*)
490      (make-date year month day)
491      expense-account
492      payment-account
493      amount
494      'taxes
495      description))))
497(define *current-invoice* (make-parameter #f))
498(define *invoices* (make-hash-table))
500(define-syntax invoice
501  (syntax-rules (service sale expense)
502    ((invoice name third-party (ymd year month day) body ...)
503     (let ((inv
504            (make-invoice name
505                          (make-date year month day)
506                          (hash-table-ref *third-parties* third-party)
507                          '())))
508       (parameterize
509        ((*current-invoice* inv))
510        (begin body ...))
511       (set! (hash-table-ref *invoices* name) inv)
512       (generate-invoice-transactions! inv)))))
515We end the expansion of the {{invoice}} macro with a call to
516{{generate-invoice-transactions!}}, which will do the task of creating
517the double-entry transactions for the invoice. Other types of summary
518structure can be added by calling additional generator procedures at
519this point. This is largely a matter of going through the invoice
520lines, handling them on a case-by-case basis to generate lists of
521transaction splits that we can append together to generate the invoice
522transaction. The case of expense lines is interesting, in that an
523extra transaction has to be generated for each expense, to record its
524initial spending, as well as a split to record the expense being
525claimed in the invoice.
527For now, let's just handle one case:
530(define (generate-invoice-transactions! inv)
531  (register-txn! (make-txn
532    (invoice-date inv)
533    (string-append "Invoice " (invoice-name inv) " for "
534                   (third-party-full-name (invoice-third-party inv)))
535    (let ((txn-balance-account
536           (third-party-balance-account
537            (invoice-third-party inv))))
538      (flatten
539       (map
540        (lambda (line)
541          (cond
542           ((invoice-expense-line? line)
543            (list)) ;; FIXME: Not implemented
544           ((invoice-sale-line? line)
545            (list)) ;; FIXME: Not implemented
546           ((invoice-service-line? line)
547            (list
548             (make-txn-split
549              (invoice-service-line-income-account line)
550              (- (invoice-service-line-amount line))
551              (invoice-service-line-description line))
552             (make-tax-splits
553              (invoice-service-line-taxes line)
554              txn-balance-account)
555             (make-txn-split
556              txn-balance-account
557              (invoice-service-line-amount line)
558              #f)))))
559        (invoice-lines inv)))))))
561(define (make-tax-splits taxes txn-balance-account)
562  (map (lambda (tax)
563         (let ((tax-type (car tax))
564               (tax-amount (cdr tax)))
565           (case tax-type
566             ((vat20 vat15 vat175)
567              (list
568               (make-txn-split
569                (find-account "taxes.vat")
570                (- tax-amount)
571                #f)
572               (make-txn-split
573                txn-balance-account
574                tax-amount
575                #f))))))
576       taxes))
579Feeding in the above example invoice, then checking out the resulting
580double-entry transaction list, shows that it worked:
583(hash-table-for-each *txns*
584                     (lambda (date txns)
585                       (for-each
586                        (lambda (txn)
587                          (printf "Date: ~A Desc: ~A\n"
588                                  (txn-date txn)
589                                  (txn-description txn))
590                          (for-each (lambda (split)
591                                      (printf "Acct: ~A Delta: ~A Notes: ~A\n"
592                                              (account-name (txn-split-account split))
593                                              (txn-split-amount split)
594                                              (txn-split-notes split))) (txn-splits txn)))
595                        txns)))
598   date: #<date> Desc: Invoice INV005 for Widget Corp
599   Acct: Delta: -800 Notes: Router setup and installation
600   Acct: taxes.vat Delta: -160.0 Notes: #f
601   Acct: clients.widgetcorp.balance Delta: 160.0 Notes: #f
602   Acct: clients.widgetcorp.balance Delta: 800 Notes: #f
604We've ended up with multiple splits for the same account, as we record
605that both VAT and the money due for the service are to come from the
606client's balance account - and other splits will add plenty more. To
607fix this, we need to write a procedure that canonicalises a list of
608splits, and call that on the splits before calling
609{{make-txn}}. Canonicalisation consists of finding all the splits that
610refer to the same account and have the same notes (be it {{#f}} or a
611string) and merging them into one with the total of the amounts. But
612I'll leave that (along with implementing bills, payments, and some
613actual reports) as an exercise to the reader... It's easy to imagine
614how to generate a VAT report from the list of transactions, by
615filtering them for membership of the required date range and looking
616for splits involving "taxes.vat", or to generate a nicely formatted
617invoice by extracting a single invoice record, or to work out the
618balance of an account at any point in time by adding up all the
619transaction splits that involve it up to that point in time. Also, the
620core engine needs to be wrapped up in a module that only exposes the
621required bindings, and hides internals.
623Having automated one's book-keeping and financial reporting, many
624operations (such as the VAT returns) can be done without involving an
625accountant; in my case, the accountant is only needed to help with the
626annual corporation tax computation and filing of official accounts,
627which requires deep understanding of the UK tax system to do
628everything properly. Having said that, if I studied the system
629properly (and tracked the changes each year), I'm sure I could
630automate that, too...
632== 9. About the Chicken Gazette
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