@hackage / stock

Stock-style deriving via coercion, with no Generic

Changelog

Changelog

0.1.0.1

  • Category via Overriding2: accept the field-keyed override forms (Con at i via M, name via M), not only the dense '[ '[ .. ] ] positional list; and fix a kind bug where a modifier's phantom parameters (e.g. Basic m a b) were left at skolem kinds.
  • Per-field override reshapes are now validated: an override that maps a field to a non-coercible modifier (e.g. Maybe via [], Int via Op) is rejected with a clear error instead of silently emitting an unsound coercion. Applies to Functor, Foldable, Traversable, Applicative (Stock1) and Category (Stock2); the other classes already validated.
  • Documentation: fixed the package-description rendering (cabal-version 3.0 needs real blank lines, not the . convention) and made the class / wrapper / companion links resolve.

0.1.0.0

Initial release.

  • A GHC type-checker plugin that synthesizes class instances for the Stock / Stock1 / Stock2 newtype wrappers, used through DerivingVia — no Generic, no hand-written boilerplate.
  • Built-in classes — Stock: Eq, Ord, Show, Read, Semigroup, Monoid, Enum, Bounded, Ix, Generic; Stock1: Functor, Contravariant, Foldable, Applicative, Generic1, Eq1, Ord1, Show1, Read1, Traversable, TestEquality, TestCoercion; Stock2: Bifunctor, Bifoldable, Eq2, Ord2, Show2, Read2, Category, Bitraversable. Traversable/Bitraversable are synthesized at the wrapper and used directly or via the one-liner traverse g = fmap unStock1 . traverse g . Stock1 (a bare deriving via can't coerce them onto your type — the result f (t b) puts the wrapper under an abstract applicative).
  • Extensible: satellite packages add new classes with no configuration change, via DeriveStock instances on the Stock.Derive SDK.
  • Per-field deriving modifiers via Stock.Override: deriving C via Stock (Override T cfg) (or the type-first synonym Overriding T cfg) rewrites individual fields' types during synthesis (per-field DerivingVia, zero-cost). Fields are addressed by name, type, or position (At); each modifier is pinned (Sum Int) or broadcast to the field's own type (Sum). The same -fplugin Stock also lowers a lowercase surface — Override T [ x via Sum, C at 0 via Product ] — to that marker form at parse time.
  • Synthesized instances verified against GHC's stock-derived twins and benchmarked to identical performance; all evidence passes -dcore-lint. Eq/Ord/Enum/Functor/Bounded/Foldable optimise to byte-identical Core (machine-checked with inspection-testing); Traversable/Bitraversable are byte-identical to the natural hand-written definition. Read (and Read1) build readPrec as GHC's derived Read does, so they are byte-faithful including the order of ambiguous infix parses.
  • Tested on GHC 9.6, 9.8, 9.10, 9.12 and 9.14 (stock-deepseq: 9.8+).