:: 6502, C64, racket

In my last few posts, I detailed some of my experience learning 6502 assembler for the Commodore 64. I started off using DASM, which seems to be quite a nice assembler, severely lacking in documentation. Then I discovered the very awesome KickAssembler, which includes a full blown scripting language on top of java, lots of other very nice features, and great documentation. This made me realise what a powerful modern assembler could be like - and perhaps I could go one step further with it.

Asi64 extends Racket to become a 6502 assembler. No need for scripting languages or half baked macro systems here - you have literally all of Racket and its amazing macro system on your side. It also has direct support for Vice, a popular Commodore 64 emulator, passing your labels and breakpoints along enabling a fluid programming and debugging cycle. Hats off to the fantasic KickAssembler, I have stolen many ideas from it :)

C64 Programming - Invader Fractal #2

:: C64, 6502, retro

In the last post we discovered how to decode 15-bit symmetric invaders into a chacrater set. This time around we will make them fractal!

The invaders from the last post occupy exactly one character each. The aim is to now select an invader at random, and then draw it one size bigger, using other random invaders as its “pixels” like this

Then, the process can be repeated again, drawing an even bigger invader which is formed by drawing even bigger “pixels” which are composed of the size 2 invaders, like this!

C64 Programming - Invader Fractal

:: C64, 6502, retro

I have recently been getting into programming the Commodore 64. It’s lots of fun to work in such a restricted environment, where you have to use various hardware tricks to achieve your goals. Every machine cycle and byte of memory counts!

I have not programmed in 6502 assembler or the C64 before. I am using the popular C64 emulator WinVice and an assembler called DASM. Having messed around a bit and learnt the basics of the instruction set and the hardware/memory layout, I programmed a couple of effects such as the basic text scroller. I have an idea in mind for my first demo, and part of it revolves around the invader fractal. I have implemented this in various langauages (F# and D being the most recent) and figured it would be a nice fit for the C64.


The invader fractal is a very simpe idea, based on the observation that the classic space invaders are symmetrical. Given a 5x5 grid, we can observe that the middle column is static, whilst columns 4 and 5 are columns 1 and 2 flipped around:

This means we can store the information for each row in just 3 bits, multiplied for each row gives us 15 bits to encode an entire invader. 15 bits gives a total of 2^15=32,768 unique invaders. “Real” space invaders are a little bit bigger than 5x5, but we will stick with their smaller cousins.

Programming in Racket #1

:: racket

Over the last few days I have been learning Racket, a language derived from Scheme.  The main selling point of Racket is its extensive macro system that lets you do everything from the simplest macros through to redefining the entire language (yes you can even get rid of the parens!).  It is a programming language programming language. In fact, Racket is more of a customisable programming language infrastructure / engine with a default language on top of it.

Secret Santa challenge in D

:: D, metaprogramming

I attended the first London meetup group for the D programming language last week with my friend David. Near the end we had a chance to try and solve a cool programming problem called the secret santa challenge.

disclaimer – I am a complete D 'lol newb' so there might be nicer stuff I could do with syntax etc! Also I have not yet fixed my syntax highlighter to include auto, mixin, assert, and others

The North Pole Type Provider: Escape from Santa’s Grotto!

:: fsharp, xmas, type providers

This post is part of the F# advent calendar, which is filled with all sorts of other cool blog posts, be sure to check it out. Thanks to Sergey Tihon for organising!

It’s Christmas!

Happy Christmas everyone! I have the honour of the Christmas Day F# advent calendar post

Thanks Tomas, ha!. I had a whole bunch of different ideas, and typically, I decided to choose the largest, most complicated one. Because of this, there is a lotof code written in just a couple of evenings. It is for the most part, badly designed, horribly written, nowhere near finished and should not be used as an example on how to write anything approaching nice F# code! /disclaimer