Using Monads for Elegant Error Handling - RubyConf 2021

Your app blows up in production. It's an outage and you're under pressure. You read the code. "How does this work? Why is this exception being caught here?" And so begins a long, stressful journey to understand how to fix your code.

Rescuing exceptions is normalised in Ruby, but it's a clumsy way of reacting to error conditions and causes your code to be difficult to reason about.

You'll refactor an existing app to use a functional style and see first hand how easy monads are to use and how they can make your code incredibly clean and expressive.

Transcript

1. Using Monads for Elegant Error Handling John Gallagher
8. Failure modes? Caught all exceptions? Customer experience?
9. Example - Address Editing Find contact Lookup postcode* Success? Render manual entry Render select Success? Render error Yes Yes No No * Postcode - zip code in the US
10. Exceptions
11. Exceptions
12. Exceptions
13. Problems Returning nil harmful Client knows too much No return value convention Customers: broken software You: doubt, decision fatigue
14. What is a Result Monad? Represents success or failure Consistent interface Wraps value or error
15. Refactor to Monads
16. Success and Failure
19. Exceptions
20. Monads
21. Exceptions
22. Monads
23. Exceptions
24. Monads
25. Convert to pipeline
26. Handle success with .fmap
29. Handle failure with .or
32. Chain .fmap and .or
35. Monads
36. Monads and Pipeline
37. Exceptions Monads
39. Turn it up to eleven!
40. Turn it up to eleven!
41. Benefits Readable pipeline Scales well Helps thinking Failures store errors
42. Drawbacks More boilerplate code More dependencies Not idiomatic Ruby More to understand
44. Quiz
45. Question 1 Answer: C
46. Question 2 Answer: A
47. Practice https://bit.ly/eleganterrors Run through the exercise Submit a PR Ask any questions
48. Thank you! John Gallagher Lead Developer, BiggerPockets Automation Consultant, Synaptic Mishap Twitter: @synapticmishap LinkedIn: @synapticmishap Github: @johngallagher
49. Do notation Try Check out the docs for Dry Monads