Chordal: a Scala DSL for music theory
Another post about my previous DSL experiments. This time, the target was a different hobby of mine: music. Chordal is another DSL experiment in Scala to represent music elements; working with Notes to create Chords, and then using those same Chords to build Progressions.
I thought "Chordal" was an original name until I found plenty of repos with the same one. Oh well.
Some of the challenges I faced came from building the AST. Music theory is a huge world with a lot of inherent structure and composition rules baked in. The atomic unit could be considered the pitch, which gains meaning once paired or grouped: two or three of them become a note, then a triad. Add one more and you've got a tetrachord. Keep stacking and you're into extended chords, which open up a lot of contexts that are genuinely hard to represent cleanly.
Then there's the diatonic vs. chromatic scale problem. The chromatic scale is useful for movement/transposition (going from one note to another by some number of steps), but that convenience comes with a catch: correct representation. Enter enharmonics, the fact that a note or chord can be spelled in different ways and still be "the same" pitch, but not the same note in context. Db and C# are a good example: same pitch, different note depending on what's around it.
