Refactor a Play application using cats and cats‑effect (cats IO)
summary
Refactors a Play Framework API by replacing Scala Future with a generic effect type F[_] using the tagless-final pattern so business logic remains pure and testable. Uses Cats EitherT to validate JSON into case classes and return domain errors as Left or successes as Right (avoiding nested flatMaps), implements concrete effects by bridging Cats Effect IO to Play’s Future to run in Play, publishes events to an event store, and demonstrates the minimal Cats typeclass constraints (Functor/Applicative/MonadError) required for each component.
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chapters (11)
- 0:00Introduction
- 1:45Example app overview
- 3:32Readability issues
- 5:46Cats and Cats-effect intro
- 7:33Replacing Futures with IO
- 9:18Error monad simplification
- 11:07Typeclassing F
- 12:34Choosing IO for prod
- 14:17Play controllers integration
- 16:04Demo and resources
- 17:49Q&A
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