Lisping the ChucKian Way

10/08/2016

I did it again! For the uninitiated, ChucK is a special-purpose programming language intended to be used for sound synthesis. While working on a college assignment, it occurred me that the language had just the minimum amount of features to be leveraged for my second MAL implementation (previously): Console/File I/O, an object system reminiscent of both Java and C++, regular expressions and arrays. How hard could it possibly be to write the probably most advanced ChucK program in existence?

This turned out to be a good deal more annoying than my first implementation. The major problem besides the language giving you minimal support for non-audio programming was that clearly nobody else did use it for a project of this size. I came to this conclusion after reporting a number of bugs that should have been absolutely obvious to anybody using the standard library for anything else than creating music.

Modules

I didn’t expect the first obstacle to be the very act of loading code from another file, something that should surely be supported well for a system also used in live programming. It turns out that live programming is a very stretchable term; what they do is more akin to hotswapping invidual code units in terms of files which is cute, but not what I need. There is a Machine.add(file) facility available from code, however it does not immediately load code from the specified file and instead post-pones loading after the current file has been loaded up.

I’ve pondered whether to create a file solely consisting of these instructions via make, then decided against it in favor of an upfront loading approach where a runner script extracts “magic” comments indicating the dependencies and boots chuck with all of them in that order and the file they originate from. While this isn’t ideal[1], it works surprisingly well.

I/O and time

Getting user input was also tricky. Initially I tried out the HID example just to find out that it would only work for special input devices as opposed to console input. Therefore I tried out the ConsoleInput class which gives a “hacked” thing to read from. Due to it having some oddities such as not accepting C-d (and therefore only being terminable with C-c which brings down the entire process), behaving incorrectly when nested and adding an extra space to the prompt, I hacked my own thing together with the KBHit class, an ASCII table and some flushing to standard output.

Speaking of printing, you would expect the manual to tell you how one does that… Instead you are told about the debug output syntax <<< foo >>>;, I’ve had to consult the VERSIONS file to learn that one can send strings to chout. Another wonderful gotcha was that due to some RtAudio bug, you can get spurious errors about your audio stream still running which mess up the prompt. The only way to get rid of them is starting the process with --silent which just runs everything as fast as possible resulting in 100% CPU usage. Fun.

Finally, I’ve hunted for a way to measure time for the performance tests, but learned that ChucK’s notion of it is more about coordination of sound. In silent mode, it is therefore useless. However not all hope is lost as you can shell out to date and retrieve its output in a hacky way: Std.system(command) doesn’t return anything useful, so you need to redirect to a file and read from it instead…

Exceptions

ChucK is somewhere between a traditional compiled and interpreted language. I did run into a good amount of exceptions, but was surprised that I couldn’t throw, create or catch any. This is saddening me as it forces one to return errors and check for them very often, be it in form of integers and out parameters (hello, C!) or a dedicated error object.

Functions

I’m pretty used to have at least some way to pass functions around and expected ChucK to be the same considering that the debug syntax had a way of printing functions. However the language doesn’t have any function type, so while you can coerce one into an Object, it won’t do you any good. Therefore I went for the C# solution and implemented functors, that is, classes with a call(args) method which one can instantiate and pass around. Yuck.

OO

While one can do Java-like OOP, it is severely limited. Considering that there are no generics, no super, no interfaces, no unions, no casting to arrays, no self-references, no automatic boxing or boxed primitives, an impoverished static keyword and no private, the resulting code is clumsy, yet has a certain air to it which I’d call “ChucKian”, like a few other people did on the chuck-users mailing list. The most impressive collection I’ve found so far is LicK.

Types

There is a strict distinction between reference and value types which require using either the @=> or => operators. While the manual insists strings are reference types, one can use => just fine on them…

While there are no hashmaps, one can use an array with string keys and store or retrieve objects of the array type. What doesn’t work though is retrieving or even iterating over the keys. For this reason I wrote a terrible hash table implementation using regular arrays.

Other

I’m not impressed by the compiler. It doesn’t catch things like missing returns, blatant type system abuse and OOP mistakes that result in segfaults or thrown assertions. While many hate Java backtraces, not having any is worse. Scoping is most certainly not lexical and forced me to pick more unique names in a few places.

Summary

I’ve dragged out this project far too long, but have been happy to learn that it is possible to implement MAL in a language as weird as ChucK. Next time I’ll hopefully pick a more featureful language, like SuperCollider

[1]The most obvious reason is that files may not contain cyclical dependencies, a less obvious one is that due to the approach of at most one class per file, one ends up with comically large command lines.