For comparison, a Pascal compiler in Racket:

https://github.com/soegaard/minipascal

Whats up with the emojis prepending the commit messages? Is that automated?

Not automated, I do it manually when writing the commit messages according to https://github.com/dannyfritz/commit-message-emoji

As much as I hate the excessive use of cutesy emoji, I can't help but be drawn to this kind of thing.

Of course, you could also just write out the prefix "Bugfix: ", "Security fix: ", etc. Less internationalized, but no table lookup required.

It also would not be hard to write a plug-in for whatever text editor, or your shell, that generates these.

If you do use these, you ought to include this link in your readme so that people know what the heck the emoji mean.

Original author already said it wasn’t automated, but just recently I did find gitmoji which does exactly that. :-)

https://github.com/carloscuesta/gitmoji

It tells what type of commit it is (a bug fix, a test related change, etc). Its not automated.

Very cool use of the Playground.

How did you get Xcode to render the box-drawing characters? Or, is that a function of printing to stdout inside of a playground?

If you mean the syntaxt tree, it is printed to the XCode output as text, I just made a screenshot and put it into to the Playground screenshot so it looks better.