TADS vs Inform - a (vaguely) in-depth comparison

It's fairly well accepted in the rec.[arts|games].int-fiction community that the two most-used languages are TADS and Inform, with, as Graham modestly points out, the latter perhaps having a slight edge. There have been some tentative and informal discussions of the differences between the two languages, but no one to the best of my knowledge has done any sort of serious point-by-point comparison of the similarities, differences, and various features of the two languages.

There is of course the seminal work in this field, the "Which Authoring System is Better" FAQ, but it focuses more on general issues in order to cover a wider selection of languages, and also doesn't give very much coverage to the day-to-day details that someone programming in the language would face; this text is aimed more at the nitty-gritty programming issues.

This evalution is divided into two parts, a "current status of the system" and "things that probably or may or might happen in the future". Each of those is divided into two sub-parts, comments on the system from the player's viewpoint and from the programmer's (although these must of necessity overlap some; I put foreign-language support into the coding section even though a French-speaking player is obviously going to be concerned with it also).

When reading this, please remember that at this time, there is only one compiler for each language, one virtual machine which each language is compiled, and no cross-machine compilers. Therefore, I will be using the language and the virtual machine entirely interchangably, and the interpreters and the virtual machine somewhat interchangably. Also, some of these responses are muddied by the fact that TADS/HTML has just come out, a much-improved interface for standard TADS games which allows various HTML-based innovations (including sound, graphics, windowing, etc). In general my comments apply to both standard TADS and TADS/HTML. I've tried to be clear when I'm speaking about just one or the other. Finally, please note that I've tried both TADS and Inform, but use TADS almost exclusively. This should suggest something both about my experience with the two systems as well as my personal biases; I've tried to be as fair as possible but advocacy has a way of slipping in sometimes :) If you have any comments on this page, feel free to mail me. I'm especially looking for evaluations/descriptions of other languages (ie, Hugo) at this level of detail.

Current Status

• Inform games files tend to be smaller, and so are the save files on the more up-to-date interpreters (ie, most of them).
• The look&feel of Inform games tends to be a little cleaner, although this is a relative judgement.
• I like TADS' parser more, although again, this is a relative judgement.
• Portability of normal interpreters is in general not an issue except on pocket machines: if you want to play a game on your Pilot or Newton or something, it has to be an Inform game. Graphics interpreters are somewhat less ported for obvious reasons: the TADS/HTML interpreter is only available on Win95 with a limited no-sound version on WinNT, while Z-Machine interpreters are available for windows/dos, amiga, and in limited form on the Mac.

Coding:

• Inform's manual is more, mm, English (as in the country (which is not entirely surprising, given the author)). I find the two manuals approximately equally useful, though. Beyond the user manual, Inform is better documented.
• TADS can produce bigger game files (ie, there's basically no upper limit on how large the game can be; Inform games can be sizable (q.v. Curses or Jigsaw or Erden) but there is an upper limit which you might well reach).
• TADS lets you do dynamic object creation. Inform makes you give a maximum number of objects of the class that will be created (and, I think, actually creates them in the game file, so they do take up space all the time. I'm not sure about this though)
• Standard TADS handles foreign languages in a somewhat less sophisticated manner than Inform does, IMO. You can write a game in Russian or Latin or Italian in Inform; it'd be much more difficult or impossible to do the same in TADS.

  But as Neil K Guy points out:
  "Minor point: HTML-TADS fully supports ISO Latin-1. So you can write games in most Western European languages. You can't do double-byte fonts, so no Asian languages that use scripts, no Arabic, Hebrew, etc. No Cyrillic either. The main problem here, however, is the currently hardcoded parser. That can make parsing many languages difficult."

• Some TADS interpreters will let the game call compiled C code. This feature is rarely useful or usable.
• Inform was developed on an Acorn, a machine which is rare outside the UK. As such, there are occasional annoyances in the compiler and language which crop up for people not using Acorns (ie, most people (but considering the majority of people use Win95 and code accordingly, they are hardly in a position to take the moral high ground)).
• Inform's source code is pretty good. TADS' source is horrid (except for the new HTML parsing stuff, which is nice). This shouldn't have too much effect unless you want to port it.
• TADS' default library is nice. Inform's default library is also nice, unless you want to modify it.
• Inform's parser is nice. TADS' parser is also nice, unless you want to change it, because you can't. There are a limited number of entry points that let you do some stuff (eg, customize error messages), but there are some things it just can't do.
• The syntax of the two languages are clearly different. This is the most important difference from the programmer's perspective, IMO, and will probably decide your preferred language. I'm fairly biased about it, but IMO TADS is clean and Inform is messy, and that's all there is to it. TADS feels like C with objects, with some parser interfaces grafted on. Inform feels like it was grown in layers. Nevertheless, it may be easier to learn piecemeal, as there are many convenient pieces to use (but the counterpoint to that, again IMO, is that once you know a little TADS you can extrapolate the rest; each new chunk of Inform is a concept unto itself and not logically or stylistically related to any other chunk).
• Finally, if you like that sort of thing, there's graphics and fancy cursor positioning and stuff. You can write a text-based version of tetris in Inform; you can't do the same in TADS. With the advent of TADS/HTML, both TADS and Inform can display graphics and play sounds and make windows. As far as I can tell, Inform's abilities in this area are superior but not as well-documented, -defined, or easy to use currently. There's also the minor issue that Inform games can't be written to use just some graphics; you have to make a commitment and compile "a graphics game", although the actual code changes required are fairly small, I think. TADS games can use graphics with virtually no change, and you can play the same game with a graphics or non-graphics supporting interpreter. In fact, TADS games currently can't even tell if they are being run on a graphics or non-graphics interpreter, which may cause problems (but this is going to be changed soon, so soon that I'm mentioning it here and not in the "future issues" section). Inform is in the middle of a change of standards; currently it's not really possible to make graphics that adhere to the old standards (which are supported by some interpreters), and no interpreters support the new standards, which are the only ones that actual games can be made with. (Also, note the portability issues mentioned above in the "playing" section)
• Oh, and Inform games compile to the same format that Infocom games used. Some people like that.

Into the Future

• The source code of TADS is available and will probably be improved. This will probably result in better portability, though perhaps still not as good as Inform interpreters, and maybe I'll like the look and feel more.
• The Inform parser may get changed. No idea. It is certainly at least theoretically changable.
• It would be possible to add string compression to TADS games which would reduce their size by a fair amount, and it would be also possible to reduce the size of their save files (although TADS' true dynamic creation makes this more difficult).
• Portability of TADS/HTML and graphics-capable Z-machine interpreters is likely to increase somewhat but will probably be restricted to the more major platforms (ie, Windows, Macintosh, Amiga, possibly X-Windows).

• The TADS documentation will almost certainly get better. The amount of example code for both languages will probably continue to increase.
• A larger upper limit on Inform games will probably be made soonish. This may or may not make them large enough to be effectively always competitive with TADS' size limit.
• Inform is unlikely to ever get true dynamically-allocated objects, in my opinion. I don't know much about this though. (It's definitely theoretically possible to support dynamic creation in the Z-machine, however).
• TADS' base foreign language support may change, though I'm a little doubtful if this is a top priority due to (as far as I see) little demand. TADS/HTML will probably become viable for foreign languages once TADS' parser gets revised.
• TADS' source will probably get much cleaner. Inform source, like I said, is already pretty good.
• Someone is planning on writing a whole new OOP Inform library. This will be cool and probably have a large impact on the language if it gets done.
• The TADS parser will be moving into the game file eventually. This will presumably make it just as flexible as the Inform parser.
• The syntax of the languages is unlikely to change substantially, or if it does, will probably exacerbate the style differences, not erase them.
• TADS' graphics/sound abilities will probably improve some. Inform's graphics/sound ease of use will almost certainly improve. You will always be required to compile into a special graphics game file as opposed to a "generic" one. Interpreters that support the new Inform graphics&sound formats should be appearing soon, allowing new-style graphics&sound games to be played.