lessons and observations

• Performance is mysterious. I initially used DList to append MIDI events but then timing showed it was the same as (++) even for huge inputs. Huh?
• There is only one new typeclass declared, and it's just for pretty-printing: Id. But maybe it's just me, I almost never use polymorphism in OO languages either. (no longer totally true)
• Excessive polymorphism leads to all sorts of annoying type errors, and type variables and class contexts bubble up (e.g. Schema cmd signature). Dummy classes (e.g. Perform.SignalBase) can help.
• Most test code is constructing test data, and pulling out the data to test afterwards. It's worth writing reusable libraries of this from the beginning! Since haskell lacks introspection, you can't write a generic diff, so when the data is large you must strip irrelevant data.

  E.g. Perform.PitchSignal_test, 'sig' constructor vs. 'unpack'.

  Derive.Schema_test.test_compile

• Having state in both fltk and haskell is really error-prone, e.g. track collapse.
• Phantom types are fun: Signal.Signal y