Scale By The Bay 2018 Unconference: Joe Kachmar
summary
Builds a Haskell pattern that restricts effects by encoding interfaces as type classes and wiring concrete implementations into a ReaderT ReaderT app newtype so production uses real IO (HTTP manager, katip logging wired via generic lens) while tests swap in mock backends. Tests use phantom-type flags to choose instances and a list-backed logger (test scribe list) that captures log output for assertions. The approach works but gets cumbersome as the number of effects grows.
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chapters (6)
- 0:00Introduction and problem
- 4:04Defining effect interfaces
- 8:19Concrete implementations and usage
- 13:15Mocking for testing
- 19:54Critique and alternatives
- 22:46Q&A and final thoughts
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