Minecraft Forums

The Adventure (What is this?)

I intend to write this post a little like a blogpost, where I will try the next step required and report back findings and tips for those interested. The mod idea is a mod update checker, yes this has been done before (once by me) however Clojure is very good at this sort of problem¹.I want the main output of this to be the learnings rather than the mod itself.
I also want to be very clear, that this may not even work out. Even if that is the case then I guess we have still learned about minecraft and Clojure.
Note¹: If anyone has another mod idea please suggest it, however think more data processing rather than adding blocks.

Why Clojure?

Clojure is a functional programming language that runs on the jvm (so has access to all Java libraries). The syntax of Clojure is a derivative of Lisp and in my opinion this coupled with it using a "pure functional" paradime makes it's syntax very clean. Furthermore unlike Java functions are "first class citizens" and the concept of Objects do not exist². I find that this also makes programs both more concise and easier to understand. I guess what it comes down to for me is that I like Clojure and I am interested to see how a minecraft mod will work. Note²: Due to the fact that all Java code can be called in Clojure this is not strictly true, it is however not the "normal" way clojure is used.

Part 1: Set-Up & Libraries

The first hurdle I had was setting up a minecraft/clojure environment. Luckily a gradle plugin exists which will allow gradle to compile Clojure code called clojuresque. So I had to add this as a dependancy to my build.gradle

dependencies {

 classpath 'clojuresque:clojuresque:1.7.0'

 classpath 'net.minecraftforge.gradle:ForgeGradle:1.2-SNAPSHOT'

 }

Add clojars as a repository

maven {

 name = "clojars"

 url = "https://clojars.org/repo"

 }

As well as enable the plugin

apply plugin: 'clojure'

The second problem I ran into is by default Minecraft download's its dependencies and Forge adds a few more, some of which are scala specific ones. To run Clojure at least one more library is required (core.clojure). I really had 3 options that I could think of:

1. Ask the Minecraft Forge developers to download clojure libraries by default as well as the ones it requires.
2. Package the clojure libraries I require inside my mod.
3. Create a "Coremod" that will download the required libraries and add them to the classpath after minecraft is started but before mods are loaded.

I doubt Minecraft Forge will agree to 1 at this early stage (with any luck down the track once we have a working prototype this might work). Option 2, although probably being the easiest will result in relatively large mods that will have to be re-downloaded each time a new version of this mod comes out. Furthermore, it doesn't scale well when (of course by when I mean if) multiple people develop Clojure mods. So I went with number 3. Luckily I do know my way around Coremods quite well. And although Clojure is my new favourite programming language, I have tones of experience in Java. Basically these are the steps required.

1. Given a list of libraries with their maven details
2. Loop through each required library
• If library has previously been downloaded do nothing
• If not, download the library and put it in a known location
• Load library using filename from above into classpath

For a minimum viable solution I am not worring too much about error handling or dependancies of libraries, the former of which I will do when this becomes more stable, the later I can manually do. Because I want this to be more about my Clojure adventures and less about the boring library stuff I will skip ahead and give the TLDR version. This worked without too much trouble. This should allow any potential users to keep a cached version of the required libraries for my mod rather than having to re-download them.
For those who are interested, here is a link to the github tag with the finished library downloader.
Stay tuned for the next step of the adventure, trying to make Minecraft Forge load a Clojure mod.