Architecture
Every freddie app has the same shape, which will be familiar to anyone acquainted with the Elm architecture. A program maintains some state and receives a stream of events. Those events are dispatched, which may result in a handler getting called. Which handler runs depends on the program state. A handler can mutate the state and return effects. Those effects are then performed.
The regular-program part is the setup: subscribe to streams of events, turn those into an enum, call let effects = state.handle(event).unwrap_or_default(), and perform each effect.
The freddie part is everything that happens inside state.handle(event). handle is a pure state transformer: state and event in, updated state and effects out. That is what makes it easy to test.