R. Matthew Emerson

OpenMCL is getting renamed to Clozure CL. Now that regular MCL is going to be released as open source software, this is proabably a good idea. It’s already the case that many people think that OpenMCL runs only on the Macintosh. In reality, it runs on PowerPC hardware under Mac OS X and Linux PPC, and on x86-64 hardware under Mac OS X, Linux, and FreeBSD.

Anyway, OpenMCL has had a kind of proof-of-concept Cocoa-based development environment for a while now, but it’s starting to get some attention.

A demonstration version of the Clozure CL development environment for the PowerPC Macintosh is available as a double-clickable application. (There’s an x86-64 version, too, but it won’t be released until Leopard comes out.)

See the announcement.

On the NeXT machine, there was a command called sndplay that would play .snd files from the command line.

It’s not too tough to put together a similar one for Mac OS X. We can play many more kinds of sounds than the old NeXT sndplay command did. On the other hand, since NSSound uses QuickTime to play some media formats, a run loop is required for sounds to keep playing, so that requires a few gyrations.

sndplay.m

(See also this cocoa-dev message)

I find that tools like Xcode are often too heavyweight when trying out little fragments of code. In these cases, it can be simpler to use the traditional Unix tools to edit, compile, and run tiny test programs. (Of course, it might be simpler for me because I’m used to the traditional Unix way.)

For instance, say that you have created a category on NSMutableArray that adds a method to reverse the contents of the array, and you’re ready to test it out.

You could create an Xcode project for this (you’d use the Foundation Tool template), but it’s also possible to use a Unix text editor (like emacs or vi) to create the file that contains your category, together with a simple main() function. (Here is an example file.)

There are basically two tricks to know. The first is that you need to create an autorelease pool before you call any methods, or else you’ll see warning messages about leaking objects. The other trick is how to compile the file, and that is simply

cc file.m -framework Foundation

Now, just run a.out. Debug, edit source, re-compile, repeat.

What’s so great about Lisp? This question is frequently asked by people who wonder what such a weird-looking language could offer.

The usual response is often “macros.” As a one-liner, this is probably a fair answer. However, it’s not very enlightening, since the questioner isn’t going to have any idea what a Lisp macro is, or what it can do. Telling someone that penicillin is great because it is an antibiotic isn’t very useful if the questioner has no idea what bacteria are or what role they play in causing illness.

The thing *I* like best about using Lisp is that it’s interactive.

My current project is a Mac OS X application written in Objective-C. I am using Apple’s Xcode developement environment, which contains numerous fancy features.

Yet, I still have an emacs running, talking to an inferior lisp via SLIME.

Sometimes I use the lisp as a calculator. Sometimes I’ll get a function working in Lisp and then re-write it in C for insertion into my application. Sometimes I’ll re-write some troublesome C function in Lisp and debug it from the lisp.

Having the ability to do this sort of work interactively and incrementally is a real pleasure. No recompiling files, no special debugger commands, just the whole Lisp environment at your fingertips all the time.

I was browsing through a copy of the New Turing Omnibus, and ran across the article on detecting primes.I grabbed an algorithms text, and implemented the Miller-Rabin primality test in Common Lisp. Read the rest of this entry »

A subscriber on cocoa-dev@lists.apple.com was asking whether there was some way to programmatically determine the default route.

The cheap and sleazy way would be to read the output of netstat, but that’s not very aesthetically appealing.

Here is some sample code, derived from the source for netstat, which will find and print the IPv4 default route.

On Mac OS X, there is a daemon called diskarbitrationd that can notifiy interested clients of the appearance of disks and filesystems. Users talk to diskarbitrationd via the Disk Arbitration framework.

For some reason, the current developer documentation doesn’t have much to say about this framework. It therefore appears to be necessary to grovel through the headers to figure out how to use it. Fortunately, the headers are well-commented.

I was able to throw together a trivial program in about 15 or 20 minutes from first looking at DiskArbitration.h. Maybe this will help someone out there.

#include <stdio.h>
#include <DiskArbitration/DiskArbitration.h>

void hello_disk(DADiskRef disk, void *context)
{
    printf("disk %s appearedn", DADiskGetBSDName(disk));
}

void goodbye_disk(DADiskRef disk, void *context)
{
    printf("disk %s disappearedn", DADiskGetBSDName(disk));
}

main()
{
    DASessionRef session;

    session = DASessionCreate(kCFAllocatorDefault);

    DARegisterDiskAppearedCallback(session, NULL, hello_disk, NULL);
    DARegisterDiskDisappearedCallback(session, NULL, goodbye_disk, NULL);

    DASessionScheduleWithRunLoop(session,
        CFRunLoopGetCurrent(), kCFRunLoopDefaultMode);

    CFRunLoopRun();

    CFRelease(session);
    exit(0);
}