musings of a Lispnik

Daniel Janus's blog

Lithium: an x86 assembler for Clojure

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Ah, the golden days of childhood’s hackage. Don’t you have fond memories of them?

I got my first PC when I was 10. It was a 486DX2/66 with 4 megs of RAM and a 170 meg HDD; it ran DOS and had lots of things installed on it, notably Turbo Pascal 6. I hacked a lot in it. These were pre-internet days when knowledge was hard to come by, especially for someone living in a small town in Poland; my main sources were the software I had (TP’s online help was of excellent quality), a couple of books, and a popular computing magazine that published articles on programming. From the latter, I learned how to program the VGA: how to enter mode 13h, draw pixels on screen, wait for vertical retrace, manipulate the palette and how to combine these things into neat effects. One of the very first thing I discovered was when you plot every pixel using sum of its coordinates modulo 40 as color, you get a nice-looking diagonal stripes effect. Because of the initially incomprehensible inline assembly snippets appearing all over the place, I eventually learned x86 assembly, too.

Back to 2012: I’ve long been wanting to hack on something just for pure fun, a side pet project. Writing code for the bare metal is fun because it’s just about as close as you can get to wielding the ultimate power. And yet, since Clojure is so much fun too, I wanted the project to have something to do with Clojure.

So here’s Lithium, an x86 16-bit assembler written in pure Clojure and capable of assembling a binary version of the stripes effect.

To try it, clone the git repo to your Linux or OS X machine, install DOSBox, launch a REPL with Leiningen, change to the lithium namespace and say:

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(run! "/home/you/lithium/src/stripes.li.clj")

FAQ

(Well, this is not really a FAQ since nobody actually asked me any questions about Lithium yet. This is more in anticipation of questions that may arise.)

What’s the importance of this?

None whatsoever. It’s just for fun.

How complete is it?

Very incomplete. To even call it pre-pre-alpha would be an exaggeration. It’s currently little more than pure minimum required to assemble stripes.li.clj. Output format wise, it only produces bare binaries (similar to DOS .COMs), and that’s unlikely to change anytime soon.

Do you intend to continue developing it?

Absolutely. I will try to make it more complete, add 32- and possibly 64-bit modes, see how to add a macro system (since the input is s-expressions, it should be easy to produce Clojure macros to write assembly), write something nontrivial in it, and see how it can be used as a backend for some higher-level language compiler (I’m not sure yet which language that will turn out to be).

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