Making music, part 1: Reading ABC notation

2013-10-29

It’s been a bit since I’ve had time to post¹, but I’ve got an interesting new project that I’ve been working on. It’s a bit more complicated, ergo spread out over a few posts, but those tend to be the more interesting posts anyway, eh?

The basic idea is that I want to be able to write and play music in Racket. One end goal would be to make a library available for the C211 class to give them something else to work with (in addition to <a href="//blog.jverkamp.com"/wombat-ide/c211-image-api/">images and <a href="//blog.jverkamp.com"/wombat-ide/c211-turtle-api/">turtles). To that end, here’s my current plan of attack²:

Write a lexer for ABC notation to turn raw text into a list of tokens
Write a parser to turn those tokens into a song (for example dealing with the interactions between key signature/accidentals and meter/note duration)
Use the rsound library on Planet2 / pkg to play back individuals notes and chords
Tie it all together to play a parsed song in ABC notation using the rsound library
(maybe): Use the rsound library to save ABC files as WAV audio
(maybe): Figure out the format and save ABC files as MIDI
(maybe): Render songs as music sheets/li>

Sounds like fun! Let’s get started.

Functions as lists

2013-10-09

Yesterday’s challenge from Programming Praxis challenges us to rebuild a data structure near and dear to any Lisper’s/Schemer’s/Racketer’s¹/functional programmer’s heart: lists. The idea presented in their sample solution uses two element vectors, directly mimicking the general internal structure of Scheme’s lists. How about we do something a bit stranger? 😄

Large scale asynchronous DNS scans

2013-09-27

On Monday we laid out a framework for converting structures into bytes. On Wednesday, we used that to enhance Racket’s UDP and DNS capabilities. Today, we’re going to take that all one step further and scan large portions of the Internet. The end goal will be to look for DNS-based on a worldwide scale.

Wombat IDE is moving to GitHub

2013-09-27

Since the rest of my code is hosted on GitHub, I figured that I probably should move Wombat IDE there as well.

To that end, we’ve moved from Google Code: wombat-ide to GitHub: jpverkamp/wombat-ide.

Extending Racket's DNS capabilities

2013-09-25

As I mentioned on Monday, I wrote my DNS-based censorship around the world–and to do that, I need a fair bit of control over the DNS packets that I’m sending back and over parsing the ones that I get back.

Extending Racket structs to bitfields

2013-09-23

Keen eyed observers may have noticed that last Friday when I posted about converting my various Racket libraries to Planet 2 packages, that there was a new package there I haven’t otherwise talked about: bit-struct. Today seems like a good time to talk about that. Theoretically, I’ll also have another post or two this week showing exactly what I’m doing with it (spoilers: it involves sending on the order of billions of DNS requests¹).

Deploy Racket libraries to Planet 2

2013-09-20

Over the last few years, I’ve managed to write a fair bit of Racket code. It’s a lovely language and an even better ecosystem for writing quick/clean code (batteries included! ). Several times throughout that, I’ve written code that I thought could be useful to others, including several libraries that I used to write my Racket Roguelike and code that I’ve used working with the C211 class at Indiana University. I’ve always said that I should turn these into packages that others can use and… I’ve finally figured it out.

Smallest consecutive four-factor composites

2013-09-19

Another post from Programming Praxis, from this past Tuesday:

The smallest pair of consecutive natural numbers that each have two distinct prime factors are 14 = 2 * 7 and 15 = 3 * 5. The smallest triplet of consecutive natural numbers that each have three distinct prime factors are 644 = 2^2 * 7 * 23, 645 = 3 * 5 * 43 and 646 = 2 * 17 * 19. What is the smallest set of four consecutive natural numbers that each have four distinct prime factors?

Diffie-Hellman Key Exchange

2013-09-14

Today we’re going to be talking about cryptography, specifically Diffie-Hellman key exchange¹. The basic idea isn’t necessarily to communicate in secret, but rather to establish the information that makes doing so much easier.

Visualizing the Monkey Grid

2013-08-30

I’m a bit behind the times, but this post from Programming Praxis intrigued me enough that I kept it in my todo list for rather a while. So let’s get around to it.

I’ll just copy the description straight from the Programming Praxis website (although there are at least two previous version:[1][2]):

There is a monkey which can walk around on a planar grid. The monkey can move one space at a time left, right, up or down. That is, from (x, y) the monkey can go to (x+1, y), (x-1, y), (x, y+1), and (x, y-1). Points where the sum of the digits of the absolute value of the x coordinate plus the sum of the digits of the absolute value of the y coordinate are lesser than or equal to 19 are accessible to the monkey. For example, the point (59, 79) is inaccessible because 5 + 9 + 7 + 9 = 30, which is greater than 19. Another example: the point (-5, -7) is accessible because abs(-5) + abs(-7) = 5 + 7 = 12, which is less than 19. How many points can the monkey access if it starts at (0, 0), including (0, 0) itself?