# AoC 2017 Day 9: Garbage Gobbler

### Source: Stream Processing

Part 1: An input stream can contain:

• groups are delimited by { and }, groups are nestable and may contain garbage or data (objects within a group are comma delimited)
• garbage is delimited by < and >, groups cannot be nested within garbage, a ! within garbage is an escape character: !> does not end a garbage segment

The score of a single group is equal to how many times it is nested (the innermost group of {{{}}} has score 3).

The score of a stream is the sum of the scores of all groups in that stream.

What is the total score of your input?

# Making music, part 3: Making noise

Last week we parsed some music. That post was in a bit of a hurry, so we had to leave off a fair few important pieces (like ties and slurs for one; chords for a rather bigger one). We’ll get to them soon, but for now we want to actually get something playing back.

# Making music, part 2: Taking shape

It’s been a bit, but as you may have noticed life is a bit mad at the moment. But I’ve still made some progress.

When we left off last time, we’d finished the first step towards making some lovely music with Racket: tokenization. Now we want to take those songs and form them into something actually approaching music.

# Making music, part 1: Reading ABC notation

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 images and 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.