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What is Mops?

Mops is a public-domain development system for the Mac. It's based on Forth, with extensive OOP extensions, along the lines of Smalltalk. It comes with a class library which gives support for all the normal Mac interface functions. While not as full-featured as PowerPlant or MacApp, say, it's very adequate for the kind of applications which might be developed by a single programmer.

Where did it come from?

Mops is derived from Neon, which was one of the first languages for the Mac that allowed actual development on the Mac itself. It's a close cousin to Yerk, which is a more "conservative" development of Neon, basically aimed at keeping up with later Macs and systems while remaining fully compatible with Neon. Mops is more "radical". It's a complete reimplementation which compiles native (68k and PowerPC) code instead of the usual Forth threaded variety. It's very fast -- about as fast as anything on the Mac in fact. It has a few other improvements over the original Neon, such as multiple inheritance, public ivars, temporary (local) objects and object references.

Where can I get it?

The most up-to-date copies of Mops can be downloaded from the website and the SourceForge project page file download area.

I highly encourage you to check the website every month or so for new updates. Some other Mops code is available, and there various other useful links there.

If you've obtained Mops from somewhere else, I recommend you check on the web site to be sure you have the latest version. There are some ancient versions around.

Where can I find Mops discussion?

The Powermops-USERS mailing list is an unmoderated discussion forum devoted to all issues relevant to using and programming PowerMops. Everyone is welcome to join, regardless of programming experience.

Another place to find discussion of Mops is the newsgroup comp.lang.forth.mac. This is not exclusively Mops, but Mops is a primary topic of discussion.

Also the MegaWolf forum <http://forums.megawolf.com/phpBB2/index.php> has a section for Mops discussion. This may be your best bet should you not happen to have newsnet access, though I don't check it very often.

There is a mailing list that for users interested in working with up-and-coming Mops releases. If you enjoy working with the cutting edge, or would just like to be kept apprised of new developments and bug fixes, consider joining this list. Instructions for subscribing to the beta list can be found at <http://lists.sourceforge.net/lists/listinfo/powermops-beta>.

There may be other places on the net with an active interest that we haven't listed here. If you should know of one, please let this FAQ's maintainer know about them!

Do you have any other sample code available, apart from what's at those locations?

Sorry, I can't help much. I've only written two "real" Mops applications myself, and I'm not free to distribute the source. Most of my Mops time has been spent on developing it rather than writing applications in it. If the above ftp and web sites don't have what you want, try posting on comp.lang.forth.mac or the MacForth Forum - maybe somebody else there can help.

Could I learn Mac programming with Mops?

You could make a good start. Mops comes with an on-line manual, which is derived from the original Neon manual. This assumes a very basic level of knowledge about programming, and none about the Mac. However to move on past the beginner stage with Mac programming, you'll really need to read some of Inside Macintosh. You can certainly keep using Mops, though!

Could I learn OOP with Mops?

Definitely! - for the same reason as in the last question. OOP was still very new when Neon came out, so the manual explains everything from a very basic level.

Can I write things like Extensions or Control Panels in Mops?

No, sorry, you can't do it. Mops only does applications, and shared libraries on PowerMacs. In fact with OSX and shared libraries, the days of Extensions etc. as such are pretty much over.

What's the minimum system I need to run Mops?

If your Mac can run Carbon applications, then you should be able to run Mops! So just about any machine running Mac OS X, Mac OS 9 (or a version of Mac OS 8 with CarbonLib installed) should do nicely!

Please note that some newer features introduced in recent releases (i.e., calling Cocoa frameworks) are specific to Mac OS X, and have no equivalent functionality on older "Classic" versions of Mac OS.

Is Mops Carbon-compliant?

It certainly is!

Does Mops run "natively" under OS X?

Yes! The latest versions of Mops run natively on just about any version of Mac OS X and Mac OS 9, as well as versions of OS8 with CarbonLib installed. (The last of the "Classic" (non-Carbon) releases is also still available for compatibility with older versions of Mac OS without CarbonLib.)

What about Cocoa?

With the release of Mops 5.6, it is now possible to call Cocoa frameworks directly from within your Mops applications on Mac OS X! (However, it is not possible to create Cocoa frameworks with Mops.)

Does Mops support the AltiVec vector extensions found on Apple's G4-equipped computers?

Yes, it does!

If you don't know what AltiVec is, take a look at <http://www.freescale.com/webapp/sps/site/overview.jsp?code=DRPPCALTVC&srch=1> for more information.

Can PowerMops do 64-bit arithmetic on 64-bit Macs?

With version 6.0, yes!

What about the new Mach-O executable format?

With version 6.0, yes!

Do the Carbon-compliant versions of Mops still support 68k machines?

Not anymore! With the release of Mops 5.6, 68k support has been largely stripped from the distribution.

If you have a 68k Mac, we now recommend you download Mops 4.0.4, which is a complete distribution for these machines. However, we're not planning any further 68k development, so this is not officially supported.

I'd like to try Mops, but I don't have a Mac.

If you have a Forth that is reasonably close to the ANS standard, you can download a package that will let you try the Mops Object model. As this is implemented entirely in higher-level Forth, it's not marvellously efficient, but it will let you try the Mops syntax. Search for the classM10.zip package.

Note that I haven't finished the heap-based object part of this package, and in 4 years nobody's asked me for it, so I don't think I'll bother.

Will Mops run natively on Intel Macs?

No. It will run under Rosetta (which allows PowerPC code to run on Intel Macs), but to run natively the code generator would need to be rewritten to target the Intel architecture. This could be done, since it's written in Mops, but would take a lot of time. Adaptation to another RISC-style architecture could be done in a fairly straightforward way. The Intel architecture, however, is basically early-1980s vintage and is CISC, not RISC. Adaptation would be, let's say, exciting and challenging. And take even more time A LOT of time. It's not time that I have any enthusiasm whatever for putting in, especially as I strongly dislike the Intel architecture.

Do you or could you have plans for some other platform, especially [insert favorite platform here] ?

Similar answer to the preceding question. Also, Mops is very closely tied to the Mac API for all its subsidiary services such as memory allocation and all the GUI stuff.

How about a version for [some embedded 68k or PPC machine] ?

Same answer as the previous question.

I tried to compile up the system, but then [whatever it was that went wrong].

The latest versions are fully built up, so unless you're involved in implementing new features, you won't need to compile them up. You just have to double-click Mops.dic (68k Mops) or PowerMops, and start using it!

I've just got the latest version, but when I double-click on Mops.dic on my 68k Mac, I get a crash.

The most usual cause of this is that you are upgrading from an earlier version of Mops, and you still have a copy of the earlier Mops nucleus around. From the Mac's point of view, "Mops.dic" is a document belonging to the application "Mops". When you double-click on "Mops.dic", the Mac system launches the application "Mops", but if you have two versions of Mops around, you can't be sure that it will fire up the latest. In fact, it probably won't. As the location of words in the nucleus will be different between versions, you can't have a new dictionary running on top of an old nucleus - you'll just get a crash. So trash the old nucleus (if you're the cautious type, save it offline first). That way, the Mac is forced to fire up the right version of Mops.

My code works fine in the Mops environment, but when I install it as an application [whatever went wrong].

There are a couple of things that could be wrong here. A common situation is if you are using a module in an installed application, but you've forgotten to put true setInstall: myModule

somewhere in your code.

That sets the flag that makes Install include it. This will happen, for example, if you're using dialogs and you've forgotten to put true setInstall: dialogMod


Another common source of problems with installed applications can happen if at compile time you're ticking words, and comma-ing the resulting execution tokens (xts) into a table, then at run time executing the words via @ EXECUTE. This might happen, e.g. if you're porting your application from another Forth. The Forth standard doesn't guarantee that this sort of thing will work in a standard system, but it's fairly commonly done anyway. In Mops there's no problem with storing an xt at run time then using it later, but it's highly dangerous to store it at compile time, save it with the dictionary, then later try to load the dictionary and use the xt. This is because in Mops an xt is simply an absolute address, and absolute addresses of locations in your code will probably change between runs, depending on where Mops or your application happens to load into the Mac's memory. The best way to handle this kind of operation is with a DicAddr, X-Addr or X-Array object. Please see the section "Addresses--relocatable and absolute" in Part II of the manual.

Can I use color in a Mops window?

You have to make the window a color window. The Window class now has a new ivar, color?, and a method to set it, setColor: which takes a boolean flag. So before you send new: or getNew: to your window, do: true setColor: myWindow

Then when you send new: or getNew:, the window will be created as a color window.

How do I plot an Icon / use the Sound Manager / use an offscreen PixMap / use the serial port / [insert favorite problem here].

Well, this is an interesting question, but as as this is a general Mac programming problem rather than something specifically to do with Mops, I'm not really here to answer this sort of question. Try posting on comp.sys.mac.programmer.help. I'm doing this in my spare time, so it's probably not right for me to be taking time to answer basic Mac programming questions. I don't have all the answers anyway. I'm certainly not a substitute for Inside Mac. Read the appropriate parts first, and if you're still stuck, try the newsgroup. There are plenty of people willing and able to help there.

I've written this nifty code, and I'd like you to look at it and tell me what you think.

I'd rather you didn't ask me that. If you go ahead and do it anyway, I'll probably give you a nice answer since I don't want to put anybody off and try to be a nice guy most of the time, but it will go very low on the priority list and almost certainly never make it to the top. Maybe consider posting it to comp.lang.forth.mac.

I tried the code for the WhizBang99 algorithm that Joe Bloggs posted the other day, but it gave an error.

It's very unlikely that I saw the code or have any idea what you're talking about. Please see above for how to submit a bug report. If I respond at all, I'm likely to be less than polite. Should I have to do detective work to find out what on earth you're talking about, when you have all the information I need at your end? Please try to help me, and then I'll be able to help you.

What about a Windows version?

Get Win32Forth (on Taygeta). It now supports much of the Mops OOP model.

I think Mops is great, but it would be even better with [insert favorite nifty feature here].

Are you volunteering? (The person with the vision gets the job.)

The Manual seems to be a bit out of date in places?

Documentation for freeware products sometimes struggles (tm).

I'm not disagreeing, but we're trying. Now the manual is in wiki format various people will be able to contribute, and this should keep the manual from getting too far behind the project. Hopefully.

Will you continue to support Mops for some time to come?

I've been doing it for 20 years now, and don't plan to stop!

Why an oddball language that isn't C++?

Try it and see how quickly you can get things done. The most popular way isn't always the best way. After all, you're using a Mac, aren't you?