Where I work, we use Haskell's type system to keep all of these boundaries in sync. All of the "services" we have extracted are indeed libraries. These librarie

Where I work, we use Haskell's type system to keep all of these boundaries in sync. All of the "services" we have extracted are indeed libraries. These libraries use type classes to interface with the core of our application which manages data persistence. This also means that each "service" can be written mostly in isolation and use a different data store (like an in-memory DB or something), depending on our needs.