optics

Optics as an abstract interface

LTS Haskell 24.17:0.4.2.1@rev:1
Stackage Nightly 2025-10-31:0.4.2.1@rev:1
Latest on Hackage:0.4.2.1@rev:1

See all snapshots optics appears in

BSD-3-Clause licensed by Adam Gundry, Andres Löh, Andrzej Rybczak, Oleg Grenrus
Maintained by [email protected]
This version can be pinned in stack with:optics-0.4.2.1@sha256:9ffd0ffb288594c3aea9535f4389a07b0361b4df02ee2b07eb4243ace85103e3,7430

Module documentation for 0.4.2.1

Used by 2 packages in nightly-2025-10-31(full list with versions):
bowtie, yggdrasil-schema

This package makes it possible to define and use Lenses, Traversals, Prisms and other optics, using an abstract interface. See the main module Optics for the documentation.

This is the "batteries-included" variant with many dependencies; see the optics-core package and other optics-* dependencies if you need a more limited dependency footprint.

Changes

optics-0.4.2.1 (2023-06-22)

  • Fix compilation of tests with GHC 9.4 and 9.6

optics-0.4.2 (2022-05-19)

  • Allow transformers-0.6 and mtl-2.3

    Note that optics-extra no longer defines Zoom instances for ErrorT or ListT when building with mtl-2.3 or later. This is because MonadState is a superclass of Zoom, and the MonadState instances for ErrorT and ListT were removed in mtl-2.3. Be watchful of this if you build optics-extra with mtl-2.3 (or later) combined with an older version of transformers (pre-0.6) that defines ErrorT or ListT. Similarly for Magnify and MagnifyMany.

optics-0.4.1 (2022-03-22)

  • Add support for GHC-9.2
  • Add is (#410)
  • Improve error messages related to the JoinKinds class (#439)
  • Port universeOf, cosmosOf, paraOf, rewriteOf, transformOf, rewriteMOf and transformMOf from Control.Lens.Plated (#379)
  • Add (%?) composition operator (#434)

optics-0.4 (2021-02-22)

  • See migration-guide-0.4.md for more details
  • Add support for GHC-9.0
  • Drop support for GHC-8.0
  • The FunctorWithIndex, FoldableWithIndex and TraversableWithIndex type classes have been migrated to a new package, indexed-traversable (#370)
  • Add adjoin, iadjoin and both to Optics.[Ix]Traversal (#332, #372)
  • Add ifst and isnd to Optics.IxLens (#389)
  • Generalize types of generic (#376)
  • Make chosen an indexed lens to see which value is traversed (#335)
  • Remove GeneralLabelOptic extensibility mechanism (#361)
  • Add gfield, gafield, gconstructor, gposition and gplate for generics-based data access (#358, #361)
  • Add support for generics-based field lenses and constructor prisms (gfield and gconstructor) to LabelOptic so they can be used via OverloadedLabels (#361)
  • Remove unnecessary INLINE pragmas to reduce compile times (#394)
  • Simplify the type of (%) using new JoinKinds and AppendIndices classes in place of the Join and Append type families (#397, #399)
  • Print missing language extensions during TH generation of labels if there are any (#352)
  • Add support for getters of rank1 polymorphic fields to optics generated with the makeFieldLabels family of functions (#365)
  • Extend support of type-changing optics generated with the makeFieldLabels family to type parameters that are phantom and applied to non-injective type families (#365)
  • Fix TH generation of optics for poly-kinded data families (#378)
  • Fix declareFieldLabels when a field type refers to a type defined in the same quote (#380)

optics-0.3 (2020-04-15)

  • GHC-8.10 support
  • Add filteredBy and unsafeFilteredBy
  • Add FunctorWithIndex, FoldableWithIndex and TraversableWithIndex instances for Const and Constant
  • Add afoldVL and iafoldVL constructors
  • Rename toAtraversalVL to atraverseOf, and toIxAtraversalVL to iatraverseOf
  • Generalise element and elementOf to construct IxAffineTraversals instead of IxTraversals
  • Change mapping to work on optic kinds other than Iso: it now supports Lens and Prism degenerating to Getter and Review respectively
  • Generalise ignored to be an IxAffineTraversal instead of an IxTraversal
  • Add singular and isingular
  • Add (^?!) operator
  • Expose Curry and CurryCompose
  • Show expected elimination forms on optic kind mismatch
  • Use stricter uncurry for better performance
  • Add hidden LabelOptic instance to postpone instance resolution
  • Add GeneralLabelOptic for pluggable generic optics as labels
  • Document monoidal structures of Folds
  • Remove proxy argument from implies
  • Add itoList
  • Improvements to TH-generated optics:
    • LabelOptic instances make optic kind a type equality for better type inference
    • LabelOptic instances for field optics work properly in the presence of type families
    • Fixed calculation of phantom types in LabelOptic prism instances
    • Better support for generating optics in the presence of kind polymorphism

optics-0.2 (2019-10-18)

  • Add non, non' and anon to Optics.Iso
  • ix can produce optic kinds other than AffineTraversal
  • Generalise type of generic1
  • Move use from Optics.View to Optics.State and restrict its type
  • Add preuse to Optics.State
  • Rename use, uses, listening and listenings to reflect the fact that they have ViewResult-generalised types
  • Add noPrefixFieldLabels and noPrefixNamer to Optics.TH
  • Move some internal definitions out to new indexed-profunctors package
  • Introduce OpticKind and IxList type synonyms for better type inference
  • Make itraverse for Seq faster for containers >= 0.6.0
  • Assorted documentation improvements

optics-0.1 (2019-09-02)

  • Initial release