This document outlines T3, which is a new software engine for writing interactive fiction. It’s only going to be of interest if you’re planning on writing interactive fiction using the TADS authoring system. This information isn’t of particular relevance to you if you’re just interested in playing IF.

 

Executive Summary:
If you’re a busy executive and can’t be bothered to read this whole thing, here’s a quick précis.

T3 is a new software engine for people who use TADS to write IF. At the time of writing (October 2001) the virtual machine is complete but the new software libraries (analogous to adv.t and std.t in TADS 2) are not. Additionally the various software interpreters for each operating system with the exception of Windows have not yet been fully updated to use the T3 environment.

There’s always a transition time involved in a brand new system such as T3. If you’re in the process of writing a new work of IF you should probably continue using TADS 2 as you always have. T3 will offer significant advantages to authors once the libraries are complete, but most games probably won’t really need them for the time being. Authors contemplating large, complex games should take a look at T3, however, as the expanded functionality of the new system may be of use to you.

Note that “T3” refers to the virtual machine itself. The TADS language and overall system are still referred to as TADS and remain relatively unchanged. The stuff the user sees - the character-based or HTML based interface - won’t look significantly different. With T3 it’s the stuff under the hood that has radically changed.

For more information have a look at the section of the official tads.org Web site dedicated to T3.

 

What is a virtual machine?
Most modern interactive fiction systems are built around machine-independent designs. So, rather than writing one copy of a given game to run under Windows, another copy to run under MacOS and a third copy to run under Linux you could simply develop a game using TADS or Inform or Hugo. This game file would be interchangeable between all three platforms. Users would simply need the appropriate interpreter (sometimes called a runtime program) for their operating system of choice in order to play the game.

This machine independent design is built around a virtual machine - a kind of software-only computer that can be ported from (rewritten for) one operating system to another. The TADS virtual machine was originally developed in 1987, with an update (TADS 2, capable of using virtual memory) released in 1992.

Unfortunately, the TADS 2 design is getting a bit long in the proverbial tooth. It was written in the days when computers only had 16-bit processors, and so can’t take advantage of modern computers quite as easily. It also evolved over a long period of time, and has been extended in all kinds of ways - taking it in directions that Mike never dreamt of back in the late 1980s. But despite these ingenious improvements, it was becoming clear that the TADS 2 architecture was becoming increasingly constraining.

 

Introducing T3
In order to solve the problems faced by the ageing TADS 2 system, Mike Roberts announced in 1998 that he would be replacing TADS 2 altogether with a totally new system, which he dubbed T3. Rather than stretching an already old design further he would start with a fresh sheet of paper and begin anew. He also took the opportunity to revise the complete TADS standard libraries.

 

Advantages of T3:
The T3 system has a number of advantages for writers of interactive fiction. Here are some of them:

• Expanded basic library.
  The basic software library that ships with TADS 2 - adv.t - covers fairly basic text adventures of the early Infocom style. But this is 2001. We may not be flying to Jupiter in rocketships, but at least we can expect far more advanced IF software libraries. And T3 delivers. The full list of improvements is too long to get into here, but includes more and richer basic object class definitions (liquids, ropes, better vehicles and rooms), sense passing, NPC interaction and so on.


• The parser is accessible.
  The TADS 2 parser was built into the interpreter and not directly modifiable by the author. Although TADS 2 contained a lot of “hooks” that enable authors to modify the behaviour of the parser, it nonetheless wasn’t fully open. The T3 parser is written in the TADS language itself.


• TADS speaks Unicode.
  Most English-language computers today use ASCII for storing textual data. Unfortunately, ASCII is a 7 (extended to 8) bit system which doesn’t support non-English languages very well. Unicode is a 16-bit coding system with full multilingual support. By using Unicode, T3 makes it easier for writers of non-English IF.


• Improved memory management.
  T3 has an extended memory model and automatic garbage collection. The former means it’s easier to write larger games and the latter makes it simpler to implement dynamic objects that are created and destroyed on the fly.


• Enhanced TADS language changes.
  T3 includes a host of language improvements, many of which will be very familiar to Java programmers. These improvements include exception handling, sublist features, arrays, vectors, improved regular expressions, break/continue labels...

  There's a full list of all the T3 improvements on the tads.org site.