Tuesday, December 18, 2007

Quis custodiet ipsos...

I don't know what this says about Lispers' attitudes toward automated testing, or toward the RT test framework, but the commonly-distributed versions of the RT test framework did not pass their own self-tests.

The apparent cause is that the introduction of a hash-table and tail-pointer in rt.lisp to efficiently find tests by name and insert new tests at the end of the test list were not matched by the updating of the rt-test.lisp to consistently construct the miniature mock-up test suite. This diff for rt-test.lisp, introduces code to dynamically rebind those variables. The patch, in addition to one putting the self-tests into a separate package, has been applied to the HEAD of the CVS repository for GNU CLISP. Note that changing the package changes the names of the tests themselves, which requires editing the expected output in the tests.

Note how powerful and convenient the dynamic binding feature of Lisp (optional, as it should be, in Common Lisp) can be: while running the individual tests, the test procedure can effortlessly construct a sandbox in which to test out the features of the test suite, without destroying the suite of tests that is being sequenced through, and automatically restoring the state of the outer test suite as each test completes, even if the inner test throws an unexpected error---all with essentially no special effort on the part of the original programmer (except, as we see, to identify all of the state that needs to be shadowed.)

Monday, December 17, 2007

Monday, December 3, 2007

System 7 Accessing Mac OS X file servers

Using my MacIvory, until now, I have been using an old Mac Powerbook running Mac OS 9 with AppleTalk file-sharing to allow me to copy files from a USB key to the Mac IIfx host running 7.6.1. Trying to access shared folders on my newer laptop running Mac OS X failed, as did sharing in the opposite direction.

Presumably, the problem is that Mac OS X uses a revision of the AFP file-sharing protocol which is incompatible with the version used by the default Mac OS 7.6.1.

It turns out there is a fix for this issue:

  1. Install Open Transport 1.1.2 (a dependency for the next step) on the 7.6.1 Mac

  2. Install AppleShare Client 3.8.3 on the 7.6.1 Mac

The Apple article on AppleShare Client 3.8.3 has more information on this release of the software.

Apparently AppleShare 3.8.8 requires System 8.

Sunday, December 2, 2007

Genera and Packages

As I alluded to in an earlier post, Symbolics Genera takes a slightly different approach to packages than most current environments (such as SLIME under Emacs).

Part of that is because, unlike GNU Emacs today, the editor and all its intelligence is running inside the Lisp environment; another part is due to Genera supporting multiple dialects of Lisp, each slightly compatible with the other.

One consequence is that Zmacs pays close attention to the "file attributes line" in your Lisp source files. (That's the line at the beginning of the file which contains the marker "-*-"). Other Lisp environments use a heuristic, like looking for the first IN-PACKAGE form.

A chicken-and-egg problem arises when loading a file that expects to be read in a particular package. What if the package doesn't exist? Well, it isn't possible to use that package to read the file. But the package itself is defined in a file.

For me this caused a bit of confusion, because if you try to load a file with a non-existent package defined in the attributes, and you have not given Genera permission to create the package, it complains that "<package name> is not meaningful as a package name in <Lisp dialect>".

You can press Resume to allow it to be created, and then the problem goes away until you try to bootstrap again without the package existing.

The answer is found in the documentation section "Specifying Packages in Programs." If the package attribute is enclosed in parentheses, it is automatically created if it does not exist. Furthermore, you can include one package name, or a list of package names, as the second element of the list in order to specify packages which this package uses.

The other way to approach this is to create a system definition file which defines the packages up front.

(Another aspect that made me more confused is that the package name was "6502", which if in the package attribute without quotes will read as an integer, which cannot designate a package. I had to muck around a bit trying double-quotes and vertical-bar escapes, in an effort to make the problem go away, before I realized the "not meaningful" was not referring to violating some non-existent rule about package names. From time to time, I would create the package and not realize that made the message go away.)