Basic Music Theory in Haskell

While doing some spring cleaning around my hard disk, I found a little Haskell program I wrote several years ago in an attempt to learn the basics of music theory. Now, I'm not a pro at writing Haskell, and I know even less about music theory, but I'm hoping that what I wrote down back then is a bit accurate. The program seems to summarize the basics quite consisely: by just having a glance at the program, I'm rediscovering some things I totally forgot about scales and chords.

For example, this is what it says about the sus4 chord:

This program might come in handy as a summary of music theory in case I forget these things again :)