Roll Your Own Shapeless
summary
Recreates core Shapeless pieces in plain Scala: builds an HList with append, implements remove, map and nth as type-level proofs resolved by implicits, uses dependent output types to carry computed types out of implicit search, and encodes polymorphic functions with an inner-case poly trait. nth needs a whitebox macro for int→Nat plus an implicit conversion workaround; implicit prioritization and companion-scope tricks resolve ambiguities. All features compile and work, but rely on compiler quirks (SI-2712, implicit search behavior) and accept practical limitations.
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chapters (13)
- 0:00Intro
- 0:32Shapeless
- 9:42Context-Dependence
- 10:45Roadmap
- 11:06HList#remove
- 12:05Implementation
- 17:28Remover
- 23:42Implicits!
- 29:43Downsides
- 30:56Exercise 3.1
- 36:20Peano Arithmetic
- 36:52Macros
- 45:02Conclusion
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