BSD-2-Clause licensed by Nicolas Frisby
Maintained by Nicolas Frisby, Ryan Scott
This version can be pinned in stack with:invariant-0.4.2@sha256:2aa4a14be3b97a3229f83ca8f5c4da178d7cda1345b26c57733e8b58bec7b00f,2988

Module documentation for 0.4.2


Hackage Hackage Dependencies Haskell Programming Language BSD3 License Build

Haskell98 invariant functors


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