Define effect interpreters dynamically using reflection

There has been recent online discussions about impredicative encoding (aka final encoding) of free monads. Capabilities-as-type-classes, as embodied by the capability library, are essentially the same thing.

About a year ago, Michael Snoyman made a blog post about the ReaderT pattern. Ostensibly, it’s a blog post about preferring to encode state as -s when you can. But that’s not how we read it. What we saw first and foremost is a story about using extensional type classes describing…