I've created this blog to share my experiences in building a Z-machine interpreter. My name is Mike Greger and I am a C# developer and a gamer. I got started with computers in the early 1980's when I became fascinated by the worlds found within so-called 'text adventures'. Some of my favorites were written by a company called Infocom.
What is a Z-machine?
Infocom created a clever way of making their games available for the many types of computers on the market at that time by designing a virtual machine now known as the Z-machine. Each game only needed to be written once, for the Z-machine. A Z-machine interpreter was then written for each platform to run the games.
Fast forward to 2009: Infocom is long gone. The Z-machine format has been reverse engineered by talented people and the specifications made available. Armed with this information developers have created Z-machine interpreters for platforms big and small.
If it's already been done, then why do it?
The short answer is because of the challenge and learning opportunities it presents. I also like to think I can improve on some things. Some time ago I set out to write my own interpreter and succeeded, sort of. My interpreter played all the infocom games just as I remembered them. However, when I first started my project I did not have a lot of programming experience. Looking back later at what I had written I found the code amateurish and not suitable for easy reuse. I decided to rebuild it and came up with a set of design criteria for a class library written in C# 3.0 which implements the Z-machine:
- Complete. Supports all features and Z-machine versions
- Easy to use and extend
- Decoupled from any particular interface (console, windows forms, WPF, etc.)
- CLS compliant
- Well documented
- Memory efficient for multiple instances
- Not overly dependent on framework types
Why write a blog about it?
In the hope that someone will find something useful, maybe for their own interpreter or other project. While the published specifications contain a lot of useful information, Z-machine behavior can be complex and seeing a working example can be beneficial. Additionally I hope to make clear why I chose certain designs, rather than just publishing source code. Code comments tend to explain how something works, not why it was written that way in the first place.
Next time: Z-machine architecture.