Why the free Monad isn't free

on YouTube ↗41m

" summary

Argues the Free Monad isn't free: it defers evaluation by building an AST-like structure (trait Free with Return/Suspend/FlatMap), then evaluates via a generic interpreter using a runFree trampoline to swap stack for heap for stack safety. Shows a to‑do DSL, test interpreters (mutable map and action log) and a production interpreter returning Option. Costs are heavy boilerplate, large pattern-match interpreters, steeper learning curve and unclear runtime hit; alternatives include loops, built-in monads, or libraries like Scalaz/Cats/Doobie/Dubey.

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" chapters (21)

1. 0:00Introduction
2. 1:47Outline
3. 2:26Mono
4. 5:33Composition
5. 6:47Functors
6. 7:11Monads
7. 12:54Free Monad
8. 16:39Why delay evaluation
9. 17:54Trampolining
10. 18:23The heap
11. 18:48Function signature
12. 21:24Writing an interpreter
13. 24:00Using multiple interpreters
14. 24:56Deferring side effects
15. 25:37Blue Skies Scala
16. 27:40Know your domain
17. 30:14Sideeffects
18. 32:23Practical use cases
19. 33:02Other examples
20. 34:11Kelleys experience
21. 37:09Questions

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