Pierre R. Mai's Miscellany

The personal pages of Pierre R. Mai

Evaluation Order in Function Forms


In this blog post Ingvar Mattsson was wondering about the printed line resulting from evaluating:

(defun frob (x) (format t 'Frob: ~a~%' x))
  (frob (defun frob (x) (format t 'New frob: ~a~%' x))

This provides an example where I think the ANSI Common Lisp standard is actually very helpful, since it often tries to go out of its way to point out things that are explicitly left undefined, instead of simply leaving them left undefined by not defining them, as many other standards (out of fear of being ambiguous) do. Quoting from the HyperSpec, Section Function Forms:

Although the order of evaluation of the argument subforms themselves is strictly left-to-right, it is not specified whether the definition of the operator in a function form is looked up before the evaluation of the argument subforms, after the evaluation of the argument subforms, or between the evaluation of any two argument subforms if there is more than one such argument subform. For example, the following might return 23 or 24.

(defun foo (x) (+ x 3))
(defun bar () (setf (symbol-function 'foo) #'(lambda (x) (+ x 4))))
(foo (progn (bar) 20))

Thus we can see that the effect of evaluating the orginal two forms is indeed undefined (as already suspected by Ingvar Mattsson) as to which function definition is called in the second form, without going to the trouble of trying to take into account possible differences between evaluation and compilation, compile-time effects of defun, etc.

Which is my long-winded way of saying a big thank you to the people involved in creating the ANSI Common Lisp standards document (with special thanks to all involved in creating, releasing and maintaining the HyperSpec online text equivalent thereof, especially of course Kent Pitman), which is one of the nicest language standards I have had the pleasure of working with and against.

WWDC 2009 Predictions


Following the “long-standing” tradition of pundits predicting what will be announced by Apple at WWDC (or other events), here are my predictions:

  1. iPhone 3GS

    I agree with John Gruber’s prediction that a faster iPhone “3GS” will be announced, and of course it will have at least 16GB and 32GB models, though I sincerely hope, but do not expect, a 64GB model that would aid in replacing my 160GB iPod Classic. Well, maybe next year.

    I also think that we are going to see something for the lower end of the market, and I suspect it is not going to be the current iPhone 3G.

  2. Snow Leopard

    Of course WWDC on the Mac side will be all about Snow Leopard, and I fully expect an announced ship date, as well as one or two currently unknown features for Snow Leopard, though probably nothing earth shattering, technically speaking.

    I doubt a new UI will be announced for Snow Leopard, with such a short lead time for developers, and announcing a new UI that is going to ship with 10.7 before 10.6 ships is out of the question.

    I fully expect Snow Leopard to be a full price paid update, i.e. $129.

  3. No Tablet

    I’d love to be proven wrong, but I don’t think an “iTablet” is ready for release. If it should be released, it would be a high-end iPhone.

    The reason I’d love to be proven wrong is not that I’d personally want a tablet (I’d rather have either an iPhone or MacBook Air, thanks very much), but it would finally put to rest all the euphoric Apple tablet-excitement. I’ve been around since before (probably) the first time in the late 80s when tablets were all the rage (remember the GRiDPad?), and with each new tablet mania each 5-8 years, (IMHO unrealistic and unclear) expectations were never ever met by the products, and they subsequently vanished in small niche markets, never to be heard of again. An Apple tablet is either going to meet the same fate, not unlikely, or it is going to revolutionize the tablet form factor into something which people can really use in practice, not merely crave in the abstract. In either case we’ll know something more about tablets and their place in the world.

  4. Cinema Displays

    I continue to expect that they’ll update the Cinema Display range sometime this year, and it is getting kind of urgent with all current products going to DisplayPort connectors, and only one matching display. However Apple has continually failed to update them, so why now? We’ll see…

Deflate: And Then There Is Chipz


So it seems the best way of finding out about lisp packages is releasing a similar package yourself ;): Right on the foot of releasing Deflate, I get to notice Chipz, a similar, but more capable package by Nathan Froyd, the release of which in early 2008 seems to have slipped my notice completely. So anyone who is interested in RFC 1951 Deflate (or even BZIP2 decompression), please have a look at Chipz as well, which is likely to better fit your needs!

Since I can’t let any benchmarking opportunity go to waste, here’s an overview of performance when decompressing a 18.6MB gzip-compressed file into 81.9 MB uncompressed form with Deflate 1.0.0, Chipz 0.7.3 and inflate.cl from Franz, version 2.6, on various CL implementations, and gzip 1.3.10:

Common Lisp
Library / Program
Deflate 1.0.0 Chipz 0.7.3 inflate.cl 2.6
(w/o CRC32)
Deflate 1.0.0
w/o CRC32
Chipz 0.7.3
w/o CRC32
gzip 1.3.10
SBCL 1.0.29 x86 (32bit) 7.42s 7.65s 17.85s 6.56s 6.99s 5.03s
SBCL 1.0.29 x64 (64bit) 6.99s 6.41s 18.35s 6.37s 5.92s
LispWorks 5.1.2 Prof. 32bit 34.78s 197.50s 32.68s 34.02s 56.79s
Clozure CL 1.3 32bit 44.89s 48.77s 13.53s 16.07s 17.71s
Clozure CL 1.3 64bit 18.06s 16.87s 13.67s 16.87s 15.40s

Since CRC-32 calculations can overshadow deflate performance itself on some implementations, and since inflate.cl does not perform CRC-32 checksum calculations at all, the columns showing Deflate and Chipz without CRC-32 calculations might be more indicative of actual deflate performance.

Note that this was all done on a MacBook Air 1.8GHz Core2 Duo under Mac OS X 10.5.7, timing was done as an average of 3 runs each.

What can be learned from the results is that 64bit implementations with their bigger fixnum range help quite a bit in performing 32bit algorithms (like CRC-32) well even without extensive/effective declaration fine-tuning or special 32bit arithmetics operators.

(Yet Another) Deflate Decompression Implementation in CL


I have finally gotten around to separating out and cleaning up the Deflate (RFC 1951) decompression routines we have been using in-house for quite some time, and released them under an X-style free license (see links below), for those who need something with a less restrictive license or better performance than is currently freely available1.

The library supports decompression of pure deflate streams, zlib-style (RFC 1950) and gzip-style (RFC 1952) streams, including optional checksum checking. The code should be fully portable across all conforming ANSI Common Lisp implementations, and has been performance tuned for SBCL and CMU CL, and somewhat for Lispworks (CRC-32 checksum code). While the performance does not reach the level of zlib/gzip (by a factor of around 3 to 3.52 on my most recent tests with SBCL), mostly due to stream I/O overhead and a not very sophisticated huffman decoder, it is eminently usable.

Support for compression and ZIP-file handling are currently not included.



  1. Since publishing this entry, I’ve been made aware of Chipz from Nathan Froyd, which achieves comparable levels of performance and is as free as Deflate; see my newer blog entry for more information.

  2. It seems that on larger files the factor is actually nearer to 1.25-1.5, see this entry for details.

Casablanca and American Civic Culture


I know it’s a little late for the holiday season, but for a nice post-holiday read I’d like to recommend Political Philosophy Comes to Rick’s: Casablanca and American Civic Culture, edited by James F. Pontuso. This collection of essays is a nice read for fans of Casablanca, of course, especially with its combination of production background information, character analysis and historical context.

More importantly its exposition of American civic culture and political philosophy against the backdrop of Casablanca can also be a refreshing reminder of certain civic values which though constantly under attack are sorely needed in any age, especially ours.

MacBook Air and the Samsung SE-T084


Another bus-powered external DVD-writer that works with the MBA is the Samsung SE-T084. It is a slot-in type drive, weighs in at around 420g and 142 x 158 x 20mm, supports DVD-RAM and Lightscribe, as well as small diameter (8cm) discs, and seems fairly sturdy in its manufacture.

MacBook Air and the LG GSA-E50L


While lots of people seem particularly interested in getting the MacBook Air Superdrive to work with non-MBA computers, I fail to understand the large appeal of this, except for aesthetic concerns: There are a number of nice external drives that will work powered by a sufficiently capable (i.e. above-spec) USB port, or a combination of those.

One of those is the LG GSA-E50L, which is only slightly larger (156 x 165 x 21 vs. 139 x 139 x 17 mm) and heavier (380g vs. 320g) than the MBA Superdrive, is a bit faster and cheaper, and offers Lightscribe and DVD-RAM support, for those that care. I’ve purchased one of those, and it works very well with the MBA from its beefed up USB port, and through its Lightscribe support I can label discs on the road without all of the pain of printed labels. Recommended.

The Mobile 4GB Memory Barrier: Broken!


It seems that, at long last, the 4GB mobile memory barrier is being broken. It turns out that certain Intel mobile chipsets do, actually, inofficially, support 2GBit chips and hence the 4GB memory modules needed for e.g. 8GB of RAM.

I just hope that support for more than 4GB of RAM will move into the mainstream sometime later this year, maybe when Intel releases their new mobile chipsets in the second half of 2008. I find it kind of strange having all 64bit Mobile Processor line-ups (Core 2 Duo and friends), yet still next to no support for actually employing that addressing power with physical memory, given the resource hoggishness of current operating systems and applications and their non-trivial working sets.

(Via Heise Newsticker.)

The MacBook Air, Airport Security and Mass-Market Appeal


I was on the road with the MBA in the last couple of weeks, traveling around the country to various clients, and the experience has been a good one, so far. I’ll write more on the computing side of things in another post, here I just wanted to note that the MBA is indeed raising eyebrows and enthusiasm wherever I take it, whether hotel bars, coffee shops, airport security, or client meetings. Even my PowerBook 17” didn’t raise that much interest when it first came out, so I really expect the MBA to be a stellar performer for Apple.

On the topic of airport security, as e.g. Michael Nygard has already noted, the X-ray signature of the MBA is indeed different enough from the ordinary for screeners to notice (though at least the European screeners I met handled this with much less fuss than the TSA screeners encountered by Michael Nygard). Which BTW seems not so surprising to me, given the design goals of the MBA, which leads to a laptop with very little electronics inside, and the rest of the enclosure containing the spread out battery. If one were to design a device that contained as much plastic explosives as possible, while still being able to function as enough of a laptop so as to fool casual tests, the design might end up looking similar, though one would probably create something with a little more volume.

Anyway, the road so far with the MBA as a main machine has been very successful, though I still sometimes long for my large 17” PowerBook display. A related nuisance I have noticed with the MBA is that connecting an external display leads to very frequent fan noise, apparently caused by the GPU circuitry working overtime (at least with my Cinema HD 23” display).

Aside from this nuisance and either a second powered USB port or a FireWire port (or a much bigger internal HD), I still have to find something about the MBA not to like. Definitely recommened for people not doing heavily media-centric stuff. Even as a developer main machine, this can pass muster, if carefully used. And as a second machine besides a Mac Pro, the MBA is likely to be enough for many more.

On a Lisp-related note: The MBA is, like all Intel-based Macs, one of the nicest modern Lisp machines, able to run all currently maintained Common Lisp implementations (even Windows-only ones ;).

LispWorks 5.1 Released


LispWorks Ltd has released LispWorks 5.1, with a long list of improvements, see the release notes for all the gory details.

Sticking out for Mac users are the following improvements:

  • 64bit Version with full Cocoa support on Leopard
  • Services and Dock menu support in CAPI
  • LispWorks as a dynamic library (on Linux as well, Windows already had this support in 5.0)
  • Support for drag and drop of text and files

Windows users get:

  • OLE embedding i.e. LispWorks as ActiveX control
  • Documented windows registry access API
  • Support for drag and drop of text and files

General improvements:

  • Compiler optimization hints
  • Various IDE and CAPI improvements