The Å-machine

The Å-machine is a virtual machine for delivering interactive stories. It is designed for stories implemented in the Dialog programming language.

As the name suggests, the Å-machine is inspired by the Z-machine. The letter Å (pronounced [ɔː], like the English word “awe”) follows Z in the Swedish alphabet. In international contexts, å can be transcribed into aa, as in “The Aa-machine”.

The Dialog compiler can produce Å-machine story files starting with version 0g/01. The filename ending is .aastory. Support for the widely used and historically important Z-machine remains, and will not go away. But stories compiled for the Å-machine look better on the web, and are smaller and potentially faster on vintage hardware (the latter claim is unsubstantiated at the moment, but it has been an important design principle).

In a sense, the Å-machine is to Dialog what Glulx is to Inform 7. It eliminates the tight restrictions on story size, and extends the basic functionality with a carefully balanced set of new features. But the Å-machine is designed to run the same stories on everything from 8-bit systems to modern web browsers. Data structures and encodings are economical, and the overall word size has not increased. Large stories are supported, but small stories still have a very compact binary representation.

Compared to the Z-machine and Glulx, the Å-machine operates at a higher level of abstraction. This improves performance on vintage hardware, both by making story files smaller, which improves loading times, and by allowing larger chunks of computation to be implemented as native machine code. The downside is that the virtual machine is more tightly coupled to the idiosyncracies of a particular high-level language, in this case Dialog.

Currently, only a single Å-machine interpreter exists. It is implemented in pure javascript, and must be combined with a frontend that handles all input and output. Two frontends are provided: A web frontend based on jquery, for publishing stories online, and a Node.js frontend for running automated tests. A tool, aambundle, can convert an .aastory file into a web-friendly directory structure, including story and interpreter, ready for deployment on a server.

Download

The release archive includes:

  • The Å-machine specification.
  • Javascript interpreter, with two frontends.
  • Source code and prebuilt binaries for the Å-machine tools aamshow and aambundle.

This software is distributed under a 2-clause BSD license.

Examples

My IFComp 2018 game Tethered running on the Å-machine.

Here is Cloak of Darkness (Dialog source code) on the Å-machine.

Posted Tuesday 4-Jun-2019 07:28

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Anonymous
Thu 6-Jun-2019 00:55
Cool stuff!! :)
Anonymous
Thu 13-Jun-2019 08:58
What you are doing is simply awesome. Keep on going.
bertjerred
Bert Jerred
Sun 16-Jun-2019 08:45
Fascinating and fun. Thank you for sharing this!