Runtime reflection
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See for background: https://github.com/fare/fci2017

Ideas of systems with observability:

1. Animation. Abstract layer: imperative language for drawing circles,
   lines, rectangles. Concrete layer: imperative language for changing
   the colour of pixels. You can migrate animations.

2. Controlling microcontrollers. Abstract layer: state machine with
   input buttons and output LEDs. Concrete layer:
   Arduino/other microcontroller assembly. You can migrate programmes
   from one microcontroller to the other.