Roll Your Own Shapeless
summary
Recreates core Shapeless primitives from scratch using Scala implicits and a handful of macros, showing concrete implementations of HList append, type-indexed remove, map via polymorphic functions in implicit scope, and an implicit macro that lifts integer literals to Peano naturals so nth indexing compiles to precise types. Demonstrates the surprising constraints and workarounds—dependent output types, aux pattern, low‑priority implicits—and shows the resulting machinery composes and works within Scala 2’s compiler quirks.
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chapters (19)
- 0:00Intro
- 0:19Miles Sabin
- 1:54Previously on Daniel...
- 4:48Context-Independence
- 8:37Type Level Functions
- 9:57Context-Dependence
- 11:32Roadmap
- 11:55HList#remove
- 12:59Implementation
- 16:04"Out" Types
- 17:59WARNING
- 19:35Remover
- 23:24HList#map
- 25:16Implicits!
- 30:45Downsides
- 31:52Exercise 3.1
- 36:55Peano Arithmetic
- 38:17Macros
- 45:45Conclusion
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