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448 lines (396 sloc) 27.7 KB [maintenance releases]

  • Fixes to dependencies and pragmas.

3.8.6 [maintenance release]

  • Fixed an issue with DefaultSignatures being used outside of the appropriate #ifdef that caused compilation issues on GHC 7.0.2.
  • Generalized the signature of prism'
  • Added \_Void and only to Control.Lens.Prism and devoid to Control.Lens.Lens.
  • Added \_Nothing to Control.Lens.Prism.
  • Added devoid and united to Control.Lens.Lens.


  • Fixed more sporadic issues in doctests, caused by carrying flags from $setup between modules.


  • Renamed strippingPrefix to prefixed, strippingSuffix to suffixed. Left the old names as deprecated aliases.
  • Fixed issues with the test suite caused by doctests carrying flags from the $setup block between modules.
  • Benchmarks now use generic-deriving rather than ghc-prim directly, like the rest of the package.
  • Added Generics.Deriving.Lens, which is now simply re-exported from GHC.Generics.Lens.


  • Added strippingSuffix and stripSuffix to Data.Data.Lens
  • Added unpackedBytes and unpackedChars to Data.ByteString.*.Lens
  • Added unpacked to Data.Text.*.Lens
  • Added (#) as an infix form of review to ease using a Prism like a smart constructor in Control.Lens.Review.


  • Added a notion of Handleable(handler, handler_) to Control.Exception.Lens to facilitate constructing a Handler from an arbitrary Fold or Prism.
  • Added a notion of Handler and catches to and Control.Monad.Error.Lens to mirror the Control.Exception and Control.Monad.CatchIO constructions.
  • Added additional doctests and documentation.
  • Improved error messages and support for types with arguments in makeFields.


  • Fixed a bug in makeFields in hierarchical modules.

  • Fixed an issue with running the doctests test suite when an older version of semigroups is installed.


  • Overall:
    • Replaced each of the different SimpleFoo type aliases with Foo' throughout. The various Simple aliases can still be found in Control.Lens.Simple but are now deprecated.
    • Made sweeping changes to Iso and Prism and Indexed lenses internally. They are now based on profunctors. This affects how you use indexed in the resulting code and dramatically changed the meaning of Overloaded.
    • Generalized combinators to pass through indices unmodified wherever possible and added indexed variants to existing combinators. There are hundreds of these changes and they would swamp this list.
  • Control.Exception.Lens
    • This module was created to add combinators and prisms that make it possible to work with GHC's extensible exceptions and monad transformer stacks more easily. There are knock-on changes in Data.Dynamic.Lens, System.Exit.Lens, and System.IO.Error.Lens.
  • Control.Lens.At
    • Moved At(at) and Contains(contains) and factored out Ixed(ix).
    • Deprecated _at and resultAt.
    • Removed various ordinal and ix combinators, which are subsumed by Ixed(ix).
  • Control.Lens.Cons
    • Consoldiated the various _head, _tail, _init and _last traversals that were scattered around the place into a pair of Cons and Snoc classes that provide _Cons and _Snoc prisms respectively, and combinators that build on top.
  • Control.Lens.Each
    • Generalized the signature of Each to permit it to provide an IndexedSetter for ((->) e).
    • Each now uses an Index type family that is shared with At, Ixed and Contains to indicate these operations are related.
  • Control.Lens.Equality
    • Added as a stronger form of Iso that can be used to safely cast.
    • Added the adverb simply, which can be used to simplify the types of most combinators in the library so they only take a simple lens, simple traversal, etc as their first argument instead. e.g. simply view forces a ~ b, s ~ t in the argument to view.
  • Control.Lens.Fold
    • Added foldr1Of' and foldl1Of'.
    • Added has and hasn't.
  • Control.Lens.Indexed
    • The various indexed combinators for each type were distributed to their respective modules. This module grew to encompass the remaining index-specifics.
    • Added index and indices, and removed iwhere and iwhereOf. Use itraversed.indices even and bar.indices (>3) instead.
  • Control.Lens.Internal
    • This module was exploded into more manageable component modules.
  • Control.Lens.Iso
    • Strict(strict) is now a Simple Iso.
    • Added magma and imagma which can be used to provide a 'debugging view' of a Traversal.
  • Control.Lens.Lens
    • Restructuring split this module out from Control.Lens.Type and merged the contents Control.Lens.IndexedLens.
  • Control.Lens.Level
    • This module was created to provide the breadth-first-search Traversals levels and ilevels which can be used to do (optionally depth-limited) breadth-first searches through arbitrary traversals reaching all leaves at finite depth in finite time. To use these in full accordance with the laws you should restrict yourself to commutative operations and finite containers, but they are useful even in the absence of these properties.
  • Control.Lens.Loupe
    • In the interest of consistency, the Loupe alias has been deprecated in favor of ALens.
    • Loupe (and ALens) are now defined in terms of Pretext rather than Context. This permits them to be cloned at a reduced cost reducing the call for ReifiedLens.
  • Control.Lens.Operators
    • Added this module for users who insist on qualified use, but want access to the operators. They can import qualified Control.Lens as Lens and import Control.Lens.Operators unqualified.
  • Control.Lens.Prism
    • Added prism' to construct SimplePrisms.
  • Control.Lens.Reified
    • Consolidated the various ReifiedFoo definitions into one module.
  • Control.Lens.Representable
    • This module was removed. Its functionality may be split out into a separate package, but currently the linear package exports is own Linear.Core module to provide this functionality. It was taking lots of useful names for little functionality and didn't feel like the rest of the API.
  • Control.Lens.Review
    • This module now factors the review functionality out of Prism and exposes unto, which is to review what to is to view.
  • Control.Lens.Setter
    • Added contramapped and argument for mapping over inputs.
  • Control.Lens.Simple
    • Removed the infix lens aliases and repurposed the module to house the now deprecated SimpleFoo type aliases, which were replaced universally with Foo'.
  • Control.Lens.TH
    • makeLenses now generates Lens' and Traversal' where appropriate
    • Added makePrisms as a generalized makeIso that automatically generates a Prism for each constructor. makePrisms generates names with an _Foo convention. This was consolidated upon throughout the library to reduce namespace conflicts between prisms and lenses.
    • Added makeFields, which generates classes for each individual field in a data type.
    • Added makeWrapped, which automatically generates a Wrapped instance for a newtype.
  • Control.Lens.Type
    • This module was repurposed to provide a single home for all the standard lens-like type aliases used when producing lenses. You still need to go to their respective modules to find the types for consuming lens-likes if you want to generate your own lens combinators
  • Control.Lens.Wrapped
    • Added wrapped' and unwrapped' for scenarios where you need the help with type inference.
  • Control.Lens.Zipper
    • Converted Zipper to walk a magma based on the original structure and to use indices from indexed traversals when restoring from tape. This also means that when zipping around within a balanced structure with ascending keys moveTo can operate in logarithmic time, but required changing the Zipper type to add the index type.
  • Data.Bits.Lens
    • Added byteAt.
  • Data.ByteString.Lens
    • Data.ByteString.Lazy.Lens now uses Int64-based indexing.
    • The Traversal for strict ByteStrings now construct a balanced tree up to a given grain size. This permits zipper based seeking to operate in logarithmic time and speeds up many traversals.
  • Numeric.Lens
    • Created. base shows and reads integers at base-2 through base-36. integral can be used as a safe fromInteger/toInteger.

3.7.6 [maintenance release]

  • Fixed an issue with the Complex Each instance.

3.7.5 [maintenance release]

  • Fixed an errant LANGUAGE pragma

3.7.4 [maintenance release]

  • Backported the API for ALens and ALens' to support snap builds on old platforms.

3.7.3 [maintenance release]

  • Removed my intra-package dependency upper bounds for my own packages. In particular this enables us to work with semigroups 0.9.
  • Switched to transformers-compat to avoid having unbuilding modules at the top of the documentation, and to ease 3rd party compatibility.
  • Updated Setup.lhs to be compatible with Cabal 1.17

3.7.2 [maintenance release]

  • Bug fix for Magnify. It was missing functional dependencies to determine its k parameter from m or n. [maintenance release]

  • Made the doctest test suite hide all but the exact versions of packages used to build this package to avoid problems with complicated user environments.
  • Removed doctests based on :t as they are fragile and break across GHC versions.
  • Fixed GHC 7.0.4 compatibility by guarding DefaultSignatures in Control.Lens.Each. [maintenance release]

  • Removed tests that will (likely) fail in the presence of hashable 1.2


  • Added preuse, preuses to Control.Lens.Fold
  • Added Each(each) to Control.Lens.Each for indexed traversal of potentially monomorphic containers.
  • Added indexing64 and traversed64 for help with large containers.
  • Generalized the type signature of choosing.
  • Exported unwrapped from Control.Lens.Wrapped.
  • Support for hashable 1.2
  • Added (??) to Control.Lens.Combinators.

  • Fixed flagging for Safe Haskell.
  • Fixed examples.
  • Cleaned up the statement of the Prism laws.

  • Corrected bounds for hashable.
  • Fixed compatibility with Haskell Platform 2011.4.0.0 -- you may have to install with --constraint="transformers =" to avoid getting new mtl and transformer versions installed.


  • Renamed Projection to Prism.
  • Implemented a complete redesign of the way Iso and Prism are handled internally. Any Iso can now be used as a Prism.
  • The isos combinator is no longer required. iso can now be used to construct an Iso.
  • Changes to the signature of from and under were necessitated by the new design.
  • Added Control.Lens.Wrapped providing a canonical isomorphism for newtypes.
  • Repurposed ala to be closer to the original design in newtype, but added au and alaf.
  • Added _magnitude, _phase and _conjugate to Data.Complex.Lens. Renamed other lenses for consistency: _realPart, _imagPart, _polar.
  • Promoted _left and _right to prisms and moved them to Control.Lens.Prism.
  • Generalized view and views to subsume the old functionality of peruse and peruses.
  • Generalized review and reviews to both return a MonadReader and to work on a Projection.
  • Added view'/views' and use'/uses' for Simple access to the environment/state.
  • Added set', a Simple version of set.
  • Added reuse : use :: review : view and reuses : uses :: reviews : views for working a Projection from the current MonadState.
  • Removed many isomorphisms for various newtypes. _const, identity, _sum, etc. Use wrapping Const, wrapping Identity, etc.
  • Removed Data.Monoid.Lens now that its newtypes are instances of Wrapped, exporting the (<>=)-variants from Control.Lens.*.
  • Renamed via to cloneIso for consistency.
  • Moved Indexed(..) to Control.Lens.Classes.
  • Renamed index to indexed to reduce conflicts with third-party libraries.
  • Added curried and uncurried to Control.Lens.Iso.
  • Added Strict(strict) for ad hoc overloading of conversions between strict and lazy variants of ByteString and Text.
  • Bug fixes for tugTo and jerkTo.
  • These no longer traverse in the wrong direction: scanl1Of, scanr1Of, mapAccumLOf, and mapAccumROf.
  • Added anon to Control.Lens.Iso.
  • Generalized the types of the Control.Lens.Zipper combinators to work with other MonadPlus instances.
  • Added withins to Control.Lens.Zipper now that they can work better with [].
  • Added singular and unsafeSingular to Control.Lens.Traversal to assert a Traversal is a Lens, a Fold is a Getter or a MonadicFold is an Action.
  • Generalized sequenceAOf_'s type to match sequenceA_.
  • Renamed up/down/left/right to upward/downward/leftward/rightward to reduce conflicts -- in particular with Control.Arrow.
  • Readded leftmost and rightmost due to the verbosity of farthest leftward/farthest rightward.
  • Added preview/previews/firstOf and deprecated headOf.
  • Added iview/iviews/iuse/iuses to Control.Lens.IndexedGetter.
  • We've generalized the type of Bazaar and provided generalized variants of partsOf, etc. that used it. [maintenance release]

  • Added support for test-framework 0.8 [maintenance release]

  • Added support for test-framework 0.7 [maintenance release]

  • Added more explicit dependencies to the doctest suite.
  • Disabled the 'expected failure' quickcheck tests that occasionally would fail with internal QuickCheck errors. [maintenance release]

  • Added explicit dependency on containers and unordered-containers to the doctest suite


  • Added upon (along with variants of it) to Data.Data.Lens, which can be used to generate a Traversal from a field accessor or any function that returns, unmodified, a single field that would be visited by template.
  • Added some missing examples/ files to the distribution.
  • Renamed Data.Bits.Lens.traverseBits to bits.
  • Removed (^!?), which was an alias for (^?!).
  • Removed the need for Trustworthy by changing the implementation of coerce for BazaarT.
  • Moved BazaarT to Control.Lens.Internal.
  • Added (<&>) to Control.Lens.Combinators.
  • element and elementOf are now indexed traversals rather than lenses and have moved to Control.Lens.IndexedTraversal. This both fixes their former partiality and lets you use chain indexed combinators with them.
  • Added elements and elementsOf as indexed traversals for ordinal indexing into regular traversals that generalize element and elementOf.
  • Renamed Data.Complex.Lens.traverseComplex to complex.
  • Changed Data.Complex.Lens.polarize to a Simple Iso, due to the RealFloat constraint causing inference problems.
  • Renamed traverseLeft and traverseRight to _left and _right respectively.
  • Renamed traverseSlice, traverseFrom, and traverseTo in Data.Sequence.Lens to sliced, slicedFrom, and slicedTo respectively.
  • Renamed traverseAt to _at in Control.Lens.IndexedTraversal.
  • Renamed traverseArray to _array in Data.Array.Lens.
  • Renamed and made the combinators in Control.Lens.Zipper more compositional to reduce third-party naming conflicts down to just left and right.
  • Renamed &= and |= to .&.= and .|.= for consistency, mutatis mutandis their related operations.
  • Added a Plated instances for Language.Haskell.TH types.
  • Renamed atIndex and atIndices in Data.Vector.Lens and Data.Vector.Generic.Lens to ordinal and ordinals to match Data.Sequence.Lens


  • Improved SafeHaskell inference.


  • Fixed a potential SafeHaskell issue where a user could use undefined to derive unsafeCoerce. You now have to import an explicitly Unsafe module and create an instance of Trustworthy for your type to cause this behavior, so if you do, it's on your head, not mine. :)
  • Renamed EvilBazaar to BazaarT.
  • Moved a lot of internals around. Most notably, Gettable, Settable and Effective have moved to Control.Lens.Classes.
  • Exposed partsOf' and unsafePartsOf' in Control.Lens.Traversal to reduce reliance on BazaarT in Control.Lens.Zipper


  • Renamed (%) to (&) and (^%) to (^&). This avoids the conflict with Data.Ratio, which was our highest priority conflict with a third party library.
  • Switched to a more liberal type for ignored
  • Removed some "isplitting" bad combinators from Control.Lens.IndexedFold.
  • Made indexed, taking, and dropping and elementOf lazier and capable of dealing with infinite traversals and infinite folds.
  • Improved Indexing to support infinite traversals and folds.
  • Removed some of the more redundant combinators from Control.Lens.Plated, which already had existing aliases in the rest of the traversal API.
  • Moved partsOf, holesOf, and elementOf into Control.Lens.Traversal.
  • Renamed query to peruse and queries to peruses. These are much less contentious names, both contain use in their name for analogy to use and uses and the word is about reading.
  • Simpler simple.
  • Added enum and non to Control.Lens.Iso.
  • Added (^?!) to Control.Lens.Fold for unsafe access to the head of a Fold.
  • Changed _head, _tail, _init and _last to traversals in Data.List.Lens and Data.Sequence.Lens.
  • Eliminated traverseHead, traverseTail, traverseInit and traverseLast.
  • partsOf and unsafePartsOf can now also be applied to a Fold yielding a Getter or to a MonadicFold yielding an Action.


  • Redefined simple and moved it to Control.Lens.Iso. Instead of using simple l you can now compose l.simple or simple.l providing more nuanced control and a more compositional API.
  • Moved the various foo# combinators used to emit cleaner core into an unexported module, Control.Lens.Unsafe. This removes MagicHash from the public API.
  • Removed the bazaar# and runBazaar# coercions that caused issues on GHC HEAD.
  • Changed the default definition of plate to uniplate from ignored.
  • Added Data.Vector.Lens and instances for Data.Vector.
  • Added support for the split package, which is now part of the Haskell platform.
  • Removed redundant Data.List.traverseList. Use itraversed or traverse instead.
  • Moved (:<->) to Control.Lens.Simple.
  • Fixed a bug in Control.Lens.TH that was causing makeIso not to work.
  • Added lifted to Control.Lens.Setter for mapping over monads.
  • Added beside to Control.Lens.Traversal.
  • Removed the operators from Data.List.Lens, they broke the overall pattern of the rest of the API, and were terrible clutter.
  • Fixed a bug that caused resultAt to give wrong answers most of the time.
  • Changed resultAt to an IndexedLens and moved it to Control.Lens.IndexedLens
  • Changed ignored to an IndexedTraversal and moved it to Control.Lens.IndexedTraversal
  • We've relinquished the name value.


  • Made elementOf lazier and moved it from Control.Lens.Traversal to Control.Lens.Plated.
  • Made holesOf and partsOf lazier to deal with infinite structures.
  • Resolved issue #75. We now generate nicer core for most Setter and Fold operations, and some others.
  • Made lenses for field access like _1, _2, etc. lazier.
  • Added Control.Lens.Loupe, which provides a limited form of Lens that can be read from and written to and which can compose with other lenses, but can also be returned in a list or as a monadic result, but cannot be used directly for most combinators without cloning it first. It is easier to compose than a ReifiedLens, but slightly slower.
  • Moved (:=>) and (:->) into Control.Lens.Simple, which is not exported by Control.Lens by default to reduce name conflicts with third party libraries.


  • Simplified the type of filtered, so that it can be composed with other folds rather than be parameterized on one. Included the caveat that the new filtered is still not a legal Traversal, despite seeming to compose like one.
  • Renamed ifiltered to ifiltering, and while it still must take an indexed lens-like as an argument, I included a similar caveat about the result not being a legal IndexedLens when given an IndexedLens. The function was renamed because its signature no longer lined up with the new filtered and the gerundive '-ing' suffix has come to indicate an operator that transformers another lens/traversal/etc. into a new one.
  • Added taking and dropping to Control.Lens.Traversal.


  • Alpha-renamed all combinators to a new scheme. Instead of Foo a b c d, they now follow Foo s t a b. This means that you don't need to alpha rename everything in your head to work through the examples, simplifies exposition, and uses s and t for common state monad parameters. Thanks go to Shachaf Ben-Kiki for the grunt work of slogging through hundreds of definitions by hand and with regular expressions!
  • Restored lenses to Trustworthy status so they can be used with Safe Haskell once more.


  • Fixed a bug in rights1 and lefts1 in Control.Lens.Zipper which would cause them to loop forever when given a 0 offset.


  • Added ?~, <?~, ?= and <?= to Control.Lens.Setter for setting the target(s) of a Lens to Just a value. They are particularly useful when combined with at.


  • Refined the behavior of substType in Control.Lens.TH to match the behavior of typeVarsEx when moving under binders.


  • Added generateSignatures option to Control.Lens.TH to allow the end user to disable the generation of type signatures for the template-haskell generated lenses. This lets the user supply hand-written haddocks and more restricted signatures.


  • Added Control.Lens.Type.simple.


  • Added Control.Lens.Zipper.
  • Added <<~, a version of <~ that supports chaining assignment.
  • Added :->, :=>, and :<-> as type operator aliases for Simple Lens, Simple Traversal, and Simple Iso respectively.


  • Added <<%~, <<.~, <<%= and <<.= for accessing the old values targeted by a Lens (or a summary of those targeted by a Traversal)
  • Renamed |> to %, as %~ is the lensed version of %, and moved it to Control.Lens.Getter along with a version ^% with tighter precedence that can be interleaved with ^.
  • Upgraded to doctest 0.9, which lets us factor out common $setup for our doctests
  • Renamed merged to choosing. Added a simpler chosen operation to mirror both.
  • Added Control.Lens.Projection
  • Renamed traverseException to exception and traverseDynamic to dynamic, upgrading them to use Projection.
  • makeClassy now places each generated Lens or Traversal inside the class it constructs when possible. This makes it possible for users to just export HasFoo(..), rather than have to enumerate each lens in the export list. It can only do that if it creates the class. If the createClass flag is disabled, then it will default to the old behavior.
  • Added performs to Control.Lens.Action to mirror views in Control.Lens.Getter.


  • Restored compatibility with GHC 7.2. This required a major version bump due to making some MPTC-based default signatures conditional.

  • Added the missing Control.Lens.Combinators to exported-modules! Its absence was causing it not to be included on hackage.


  • Generalized the signature of Getting, Acting and IndexedGetting to help out with the common user code scenario of needing to read and then write to change types.
  • Documentation cleanup and additional examples.
  • Renamed au to ala, introducing further incompatibility with the newtype package, but reducing confusion.
  • Removed need for Data.Map.Lens and Data.IntMap.Lens by adding TraverseMin and TraverseMax to Control.Lens.IndexedTraversal.
  • Flipped fixity of ~: and <~:
  • Added ++~, ++=, <++~ and <++= to Data.List.Lens in response to popular demand.
  • Added |>, <$!> and <$! to Control.Lens.Combinators, which exports combinators that are often useful in lens-based code, but that don't strictly involve lenses.
  • Added an HUnit-based test suite by @orenbenkiki


  • Fixed bugs in Traversal code-generation.


  • Added build option -f-inlining to facilitate building with the various TH 2.8 versions used by GHC 7.6 and HEAD.
  • Added build option -f-template-haskell for testing without template haskell. (Users should be able to assume TH is enabled; use this only for testing!)
  • Added support for generating a Traversal rather than a Lens when multiple fields map to the same name or some constructors are missing a field.
  • Removed _ from the lens names in System.FilePath.Lens.
  • Added iwhere, withIndices, withIndicesOf, indices and indicesOf to ease work with indexed traversals
  • Added assign as an alias for (.=) in Control.Lens.Setter.
  • Added ~:, =:, <~: and <=: to Data.List.Lens


  • Added Control.Lens.Plated, a port of Neil Mitchell's uniplate that can be used on any Traversal.
  • Added Data.Data.Lens with smart traversals that know how to avoid traversing parts of a structure that can't contain a given type.
  • Added Data.Typeable.Lens with _cast and _gcast like traverseData
  • Renamed IndexedStore to Context now that it is used in user-visible locations, and since I also use it as uniplate's notion of a context.
  • Renamed Kleene to Bazaar -- "a bazaar contains a bunch of stores."
  • Added Comonad instances for Context and Bazaar, so we can use stores directly as the notion of an editable context in uniplate
  • Compatibility with both sets of template haskell quirks for GHC 7.6.1-rc1 and the GHC 7.6.1 development head.
  • Renamed children to branches in Data.Tree.Lens.
  • Added At and Contains to Control.Lens.IndexedLens.
  • Added FunctorWithIndex, FoldableWithIndex, and TraversableWithIndex under Control.Lens.WithIndex
  • Added support for unordered-containers.

  • GHC 7.6.1 development HEAD compatibility (but broke 7.6.1-rc1)

  • Haddock cleanup


  • Added the indexed Kleene store to Control.Lens.Internal
  • Moved Gettable, Accessor, Settable and Mutator to Control.Lens.Internal
  • Added cloneTraversal to Control.Lens.Traversal
  • Renamed clone to cloneLens in Control.Lens.Type
  • Generalized the type of zoom to subsume focus.
  • Removed Focus(..) from Control.Lens.Type.
  • Factored out Control.Lens.Isomorphic.
  • Moved many private types to Control.Lens.Internal
  • Added conFields to Language.Haskell.TH.Lens.
  • Added System.FilePath.Lens.


  • Added missing {-# INLINE #-} pragmas
  • Renamed meanwhile to throughout in Control.Parallel.Strategies.Lens
  • Added Magnify to Control.Lens.Getter.
  • Added Zoom to Control.Lens.Type.


  • Added <&=, <&~, <|=, and <|~
  • Moved <>~, <<>~, <>=, and <<>= to Data.Monoid.Lens
  • Template Haskell now uses eager binding to avoid adding dependencies.


  • Renamed adjust to over
  • Added au, auf and under
  • Added Data.Monoid.Lens
  • Increased lower dependency bound on mtl for cleaner installation.
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