BSD-2-Clause licensed by Nicolas Frisby
Maintained by Nicolas Frisby, Ryan Scott
This version can be pinned in stack with:invariant-0.5.3@sha256:e430340b5f4248159f9fd217c506946887b4ff8f2c7a3819c3d4f06bcb195e6a,3323

Module documentation for 0.5.3


Hackage Hackage Dependencies Haskell Programming Language BSD3 License Build

Haskell98 invariant functors


0.5.3 [2019.05.02]

  • Implement foldMap' in the Foldable instance for WrappedFunctor when building with base-4.13 or later.

0.5.2 [2019.04.26]

  • Support th-abstraction- or later.
  • Only incur a semigroups dependency on old GHCs.

0.5.1 [2018.07.15]

  • Depend on QuickCheck-2.11 or later in the test suite.
  • Some Haddock fixes in Data.Functor.Invariant.TH.

0.5 [2017.12.07]

  • Data.Functor.Invariant.TH now derives invmap(2) implementations for empty data types that are strict in the argument.
  • When using Data.Functor.Invariant.TH to derive Invariant(2) instances for data types where the last type variables are at phantom roles, generated invmap(2) implementations now use coerce for efficiency.
  • Add Options to Data.Functor.Invariant.TH, along with variants of existing functions that take Options as an argument. For now, the only configurable option is whether derived instances for empty data types should use the EmptyCase extension (this is disabled by default).

0.4.3 [2017.07.31]

  • Add Invariant(2) instances for Data.Profunctor.Yoneda.Yoneda.

0.4.2 [2017.04.24]

  • invariant.cabal used to incorrectly state the license was BSD3 when it was in fact BSD2. This is now fixed.


  • Fix the Invariant V1 instance so as to seq its argument
  • Allow building with template-haskell-2.12


  • Allow TH derivation of Invariant(2) instances for datatypes containing unboxed tuple types
  • Ensure Invariant(2) instances are in-scope when importing Data.Functor.Invariant
  • Add Invariant and Invariant2 instances for Kleisli and Cokleisli
  • Add Category and Arrow-like instances for WrappedProfunctor


  • Rewrote Data.Functor.Invariant.TH’s type inferencer. This avoids a nasty GHC 7.8-specific bug involving derived Invariant(2) instances for data families.
  • Add Invariant instances for Data.Complex.Complex, Data.Monoid.Product, and Data.Monoid.Sum


  • Require bifunctors-5.2 and profunctors-5.2. Add Invariant(2) instances for newly introduced datatypes from those packages.
  • Add ProfunctorFunctor, ProfunctorMonad, ProfunctorComonad, Mapping, and Traversing instances for WrappedProfunctor
  • Add StateVar as a dependency. Add Invariant instances for StateVar and SettableStateVar.
  • Add Invariant instances for URec (added to GHC.Generics in base-


  • Add genericInvmap function (and make it the default implementation of invmap for Invariant instances) on GHC 7.2 or later
  • Make Tagged instance poly-kinded


  • Add Foldable and Traversable instances for WrappedFunctor
  • Fixed build on GHC HEAD


  • Support deriving Invariant and Invariant2 instances with Template Haskell
  • Added invmapFunctor, invmapContravariant, invmap2Bifunctor, and invmap2Profunctor to make defining Invmap and Invmap2 instances somewhat easier
  • Added WrappedFunctor, WrappedContravariant, WrappedBifunctor, and WrappedProfunctor data types to allow use of invmap and invmap2 for data types that aren’t Invariant or Invariant2 instances.
  • Added Invariant instances for lazy ST, ArrowMonad, Handler, Identity, First, Last, Alt, Proxy, ArgDescr, ArgOrder, and OptDescr
  • Added Invariant and Invariant2 instances for data types in the array, bifunctors, containers, profunctors, semigroups, stm, tagged, transformers, and unordered-containers libraries


  • Add Invariant instances for Dual and Endo


  • Bump contravariant upper version bounds


  • Initial commit