Composable event sourcing with monads
summary
Claims that event sourcing becomes an implementation detail by lifting command results into a Sourced monad that replays each emitted event immediately, accumulates them like a writer monad, and threads the in-memory state through for composition. Implements helpers and a case class in Scala (references cats / scalaz) and a turtle demo to show composing commands into atomic multi-event persistence, enabling optimistic locking and declarative, testable mutation; code and slides live in the repo.
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chapters (12)
- 0:00Introduction
- 1:47Building blocks
- 6:31Recap
- 6:41What we want
- 7:13Why compose
- 8:12Alternative approach
- 8:47Multiple events
- 10:13Limitations
- 11:07Replaying intermediate events
- 11:29Automating replies
- 13:13Flatmap method
- 17:18update multiple instances
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