This Week’s Program: Jan 11 - Jan 15

Alan Rickman, too. With the passing of such creative forces, what more can we do than ensure our own creative energies don’t go to waste?

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On Monday, on my personal website, I added a lightning bolt in the style of Aladdin Sane. I reverted this commit on Tuesday

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Last week, I wrote a fair bit about asynchrony in this program, and the need to provide an imperative, linear sequences at the edges. Gary Bernhardt describes this kind of ethos as Functional Core, Imperative Shell. I also wrote about CSP (Communicating sequential processes) and how channels and queues are effective at coordinating concurrent execution.

This week, I brought in core.async to see how this would work in practice. It turns out it doesn’t do much different. This program is almost the exact same as using the promise based implementation. I cleaned up some of this code in the next commit.

In the 2-arity play function we create a channel that is passed into the temporal recursive arity (same as the promise). When the melody has completed, the tail call writes to the channel. This is a blocking operation if there is nothing reading from the channel, but because Overtone’s scheduling happens off the main thread, that doesn’t matter. We just need a way to signal back up to the caller that the song has completed playing. Back in the 2-arity function, we read from that channel in the context of a go block: an inversion of control thread. The go block returns a channel of its own that holds the value of its computation. So calling play in its 2-arity form is asynchronous and returns a channel. When you read that channel, it blocks until the song has completed playing. Exactly like the promise implementation.

The thought occurs to me that I might be doing it wrong. I think core.async is still rad, though, and I’m going to keep it around to experiment on.

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Instead of writing my recording to the same file every time I run the program, I record to a tempfile. This file will be cleaned up whenever tempfiles on the system get cleaned up. I think this is the first bit of Java interop I’ve done in this program so far.

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My first macro! I’ve been scared of macros for a long time and have been actively avoiding their creation. Now I see that they’re not that bad. Here, I make a macro to make a recording of a song to a path. The song argument is called “out” assuming that it’s a core.async channel and performs a blocking read within the returned form. I made this a macro, and not a normal function, because I wanted to pass in the call to the play function without it being evaluated immediately. It’s Lisp! Code is data! The little sigils and reader sugar that you see in macros is for quoting forms and generating symbols.

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Here, I am preparing for next week. Guess what I’ll be doing.

He’s told us not to blow it
Cause he knows it’s all worthwhile

– Mark