Module outside 

The three things the engine works against that are not its own state. Where policy is read from, what opens a content file, and how the person is spoken to. They travel together because they are chosen together — once, by main, from what the machine turns out to be — and because the engine passes all three down the same path: concept 10 puts the policy decision immediately before the launch, and concept 5.1’s warning is said about the same content file in the same breath.

Held as trait objects rather than as type parameters. The alternative threads three generics through every signature from the front door down to the session, so that a program which picks its implementations at startup can pretend it knew them at compile time.

Structs

Outside

What the engine has been given to work with.