nix-playgraound/notes/014-haskell-learning-path.md

Haskell Learning Path

This note links the Haskell examples in a suggested order from first project structure through intermediate language and application patterns.

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1. Suggested Order

1. 05-haskell/: a small Cabal library, executable, test suite, and dev shell
2. 06-haskell-shellfor/: a Haskell package set override and a shellFor-based dev shell
3. 07-haskell-deps/: external Haskell libraries through Cabal build-depends
4. 08-haskell-adt/: algebraic data types, records, and pattern matching
5. 09-haskell-newtype/: newtype, smart constructors, and validation
6. 10-haskell-effects/: ReaderT, Except, and constrained application logic
7. 11-haskell-typeclasses/: custom type classes and per-type instances
8. 12-haskell-parser-combinators/: parser combinators with Megaparsec
9. 23-haskell-maybe-either/: optional values, required-field errors, and layered request validation
10. 24-haskell-deriving/: deriving strategies for ordering, enumeration, and wrapper behavior
11. 25-haskell-state/: pure stateful planning with global and per-environment counters
12. 26-haskell-quickcheck/: property testing for a non-trivial normalization function
13. 27-haskell-aeson-roundtrip/: explicit JSON instances and round-trip checks
14. 28-haskell-applicative-validation/: accumulated field validation with an Applicative error type
15. 29-haskell-foldmap-summary/: monoidal event aggregation with one foldMap pass
16. 30-haskell-traverse-resolution/: batch resolution of requests through traverse
17. 31-haskell-writer-audit/: rollout logging with Writer
18. 32-haskell-nonempty-waves/: rollout planning with NonEmpty
19. 33-haskell-optparse-cli/: command-line parsing with optparse-applicative
20. 34-haskell-dependency-order/: dependency-ordered planning with cycle checks
21. 35-haskell-monad-chaining/: dependent rollout approval with monadic Either
22. 36-haskell-map-set-modeling/: access-policy modeling with Map and Set
23. 37-haskell-transformer-stack/: composed effects with ReaderT, ExceptT, and Writer
24. 38-haskell-generic-json/: generic JSON instances with Aeson options

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2. What to Focus on at Each Step

• 05-haskell/: how a Cabal package becomes a flake package, app, dev shell, and check
• 06-haskell-shellfor/: when a Haskell-specific dev shell is more useful than a generic shell
• 07-haskell-deps/: why Cabal stays the source of truth for package dependencies
• 08-haskell-adt/: how to model a problem with constructors before writing behavior
• 09-haskell-newtype/: how to move validation to the boundary and protect the domain model
• 10-haskell-effects/: how to separate configuration, logic, and failures
• 11-haskell-typeclasses/: how to abstract shared behavior across several types
• 12-haskell-parser-combinators/: how to build a small language from reusable parser pieces
• 23-haskell-maybe-either/: how optional fields and validation errors play different roles
• 24-haskell-deriving/: how derived behavior depends on constructor and field layout
• 25-haskell-state/: how to thread evolving planning state without leaving pure code
• 26-haskell-quickcheck/: how to test invariants across many generated inputs
• 27-haskell-aeson-roundtrip/: how to keep domain values and JSON formats aligned
• 28-haskell-applicative-validation/: how to report several field errors without stopping at the first one
• 29-haskell-foldmap-summary/: how to express batch aggregation through monoidal summary fragments
• 30-haskell-traverse-resolution/: how to sequence per-request resolution across a whole batch
• 31-haskell-writer-audit/: how to compute a result while accumulating ordered audit output
• 32-haskell-nonempty-waves/: how to encode “at least one rollout step” in the type
• 33-haskell-optparse-cli/: how to parse a real CLI into typed commands
• 34-haskell-dependency-order/: how to derive a correct deployment order from dependencies
• 35-haskell-monad-chaining/: how to express fail-fast workflows where each step depends on earlier results
• 36-haskell-map-set-modeling/: how to use Map and Set as primary domain structures, not just helpers
• 37-haskell-transformer-stack/: how to combine several effects in one concrete workflow
• 38-haskell-generic-json/: how to reduce JSON boilerplate without giving up a deliberate shape

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3. Related Notes

• notes/007-haskell.md
• notes/008-haskell-shellfor.md
• notes/009-haskell-dependencies.md
• notes/010-haskell-adts.md
• notes/011-haskell-newtypes.md
• notes/012-haskell-effects.md
• notes/013-haskell-typeclasses.md
• notes/015-haskell-parser-combinators.md
• notes/026-haskell-maybe-and-either.md
• notes/027-haskell-deriving.md
• notes/028-haskell-state.md
• notes/029-haskell-quickcheck.md
• notes/030-haskell-aeson-roundtrip.md
• notes/031-haskell-applicative-validation.md
• notes/032-haskell-foldmap-summary.md
• notes/033-haskell-traverse-resolution.md
• notes/034-haskell-writer-audit.md
• notes/035-haskell-nonempty-waves.md
• notes/036-haskell-optparse-cli.md
• notes/037-haskell-dependency-order.md
• notes/038-haskell-monad-chaining.md
• notes/039-haskell-map-set-modeling.md
• notes/040-haskell-transformer-stack.md
• notes/041-haskell-generic-json.md