You can use Subversion to track the OpenMCL sources.

First, check out an initial copy.

$ svn co http://svn.clozure.com/publicsvn/openmcl/trunk/ccl
A    ccl/l1-fasls
A    ccl/l1-fasls/.cvsignore
A    ccl/LICENSE
A    ccl/cocoa-ide
A    ccl/cocoa-ide/processes-window.lisp
A    ccl/cocoa-ide/hemlock
A    ccl/cocoa-ide/hemlock/hemlock11.cursor
A    ccl/cocoa-ide/hemlock/website
A    ccl/cocoa-ide/hemlock/website/index.html.in
.
.
.
A    ccl/examples/addressbook.lisp
A    ccl/examples/gtk-minesweeper.lisp
A    ccl/examples/.cvsignore
 U   ccl
Checked out revision 7568.
$

You need a lisp kernel and a heap image so you can compile the sources. Grab the most recent snapshot tarball from  ftp://clozure.com/pub/testing/ and unpack it somewhere. Copy the lisp kernel and the heap image (dx86cl64 and dx86cl64.image if you're running x86-64 Leopard) over to where you just checked out the sources.

Next, copy over the interface databases from the snapshots. Just copy the .cdb files.

For example, on an x86-64 Leopard system, you'd do something like this:

$ cd /path/to/snapshot/ccl
$ cp darwin-x86-headers64/libc/*.cdb /path/to/svn/ccl/darwin-x86-headers64/libc

See UpdatingFromSource for information on how to get the x86-64 interface files for Cocoa.

Go back to your sources that you checked out with Subversion, and rebuild the lisp. Again, on x86-64 Leopard:

$ ./dx86cl64
Welcome to OpenMCL Version 1.1-r7527M (DarwinX8664)! (or whatever)
? (rebuild-ccl :force t)

There might be some compiler warnings, and if there's a CERROR complaining about redefining a constant or something, it should be safe to continue from it.

Now you've got an up-to-date OpenMCL. Whever you want, tell Subversion to update the sources.

$ svn update
U     some-file.lisp
Updated to revision xxxx.

After updating, rebuild the lisp as outlined above.

See also: UpdatingFromSource