The Setup

There's this program called "OCEmu". It's a emulator for a Lua framework originally created for a Minecraft mod of all things. That mod called "Open Computers" allows the user to write Lua to control a late 80's style terminal computer inside the game with surprisingly time accurate limitations. To understand the depth we're speaking of here, your computers need hardrives, EEPROMs, RAM, CPUs, GPUs and more to function correctly and you get to write your own bios and operating system for them. OCEmu then, emulates these computers allowing you to work with the neat framework without needing to play Minecraft.

The Problem

This framework is great and all but there's just one thing that's always bothered me about it. It only runs Lua! And as anyone who's worked with Lua for any extended period of time can attest to, it's just a pain to deal with sometimes...

• No type checking

• Varying numbers of both arguments and return values from functions

• all indexing operations begin at 1 instead of 0

• No language support for OOP

Though these qualities can be desired in some applications of Lua i feel it doesn't suit my uses very well as i develop these operating systems in it... So i decided to make my own language on top of Lua and extend it so that it's less painful for me to use the framework. 

Plus, it's also just a great excuse to learn more about compilers!

The Design and Implementation

I wanted to keep the language as simple as possible so that I could develop a finished product in a reasonable amount of time. In this goal I chose to use Lua as a base for my own language. The idea being that I can simplify all the stages of the compiler by simply copying function blocks from source to output. removing any need to parse them as long as I leave the syntax inside function blocks unaltered.

Since this entire language is going to be more or less based around adding OOP to Lua I first thought I'd name the language LuaC and have C stand for Class. But after realizing that the .luac extension is apparently already in use by compiled Lua files i settled for the name LuaZ as it sounds some-what similar.

The first feature to add is classes! I took a lot of inspiration from C# while making the compiler and so I chose to add the "class" keyword to the language after which the "field", "function", or "prop" keywords could occur before ending the class with the "end" keyword in the classic Lua spirit. 

The "field" keyword simply adds a instance variable to the class with a given name and start value.

The "function" keyword has the same syntax as a normal Lua function. The only difference being that this variant of function acts as a member method for the class it's inside and has the benefit of allowing some type checking through the use of a <> delimiter for any given argument with allowed types comma separated inside it.

The "prop" keyword adds a C#-style property to the class instance. When accessing it, it looks just like a field but invokes the "get" and "set" functions when you try to read or write to it. the setter also gets a hidden argument named "value" passed to it holding what the caller wants to set the property to. This argument can be renamed and type checked exactly as with functions by simply adding parentheses after the "set" keyword and adding the argument inside.

any of these 3 keywords can also be prefixed with static to instead add them globally on the class itself.

Beyond the class feature, i also wanted all current Lua files to be valid LuaZ files. To achieve this i also allow arbitrary Lua code outside any class blocks.

I also added a "using" keyword to replace the normal Lua "require" function so that the language could look at file cross referencing and help resolve cyclic includes for me.

After a lot of learning and working on it i eventually managed to implement this language spec and write a compiler for it in C# taking in a file or folder of LuaZ source code and spitting out a new folder of pure Lua files full of function calls to a "ClassBuilder" object I've written that acts as a runtime or standard library of sorts. When invoked, this object builds up the class before returning the final class object.

For a brief overview of how i use this language: Most LuaZ files begin with a set of using statements to pull in dependencies before running some normal Lua code to set up things like settings and lookup tables before beginning a class block, implementing a class, and then ending with a short Lua block after the class block to return the class object from the file so that it may be used by other files.