This library uses GHC.Generics to derive efficient optics (traversals, lenses and prisms) for algebraic data types in a type-directed way, with a focus on good type inference and error messages when possible.
The library exposes a van Laarhoven interface. For an alternative interface, supporting an opaque optic type, see
generic-optics.
Changes
generic-lens-2.0.0.0 (2020-02-11)
Drop support for GHC < 8.4
Better inference for field'
Param traversal now properly recurses deeply (#88)
Reorganise internals (see generic-lens-core)
Breaking API changes:
HasTypesUsing now takes 4 params
Removed HasConstraints traversal
generic-lens-1.2.0.1
Give HasAny/AsAny the same VTA behavior on 8.6 and 8.8 (Ryan Scott)
generic-lens-1.2.0.0
Add HasTypesUsing and HasTypesCustom for custom traversals (Lysxia)
Improve type errors when no Generic instance is defined
types now supports Text by default
Breaking API changes
HasType now includes a reflexive case so that every type ‘contains’ itself (Matt Parsons)
AsSubtype and Subtype now include a reflexive case so that every type is a subtype of itself
generic-lens-1.1.0.0
Fix regression in type inference for polymorphic optics
Add HasField0, HasPosition0, AsConstructor0, HasField_, HasPositon_, and AsConstructor_ (Lysxia)
types now supports Data.Word and Data.Int (Lysxia)
Add Wrapped iso for newtypes (Isaac Elliott)
Expose internals through Data.GenericLens.Internal
Add labels for prisms (Daniel Winograd-Cort)
generic-lens-1.0.0.2
Fix compile-time performance regression
generic-lens-1.0.0.1
Remove dump-core dependency
Relax upper bound on criterion (#42)
generic-lens-1.0.0.0
Traversals (types, param, constraints)
Prisms are now optimal too
Monomorphic versions of lenses and prisms also included
Breaking API changes
projectSub now returns Maybe sub instead of Either sup sub (#21)
generic-lens-0.5.1.0
Infer input type from result type (#25)
Allow changing of multiple type parameters (#24)
Allow changing of type parameters that have kinds other than * (#23)
Fix error message in subtype lens
generic-lens-0.5.0.0
Lenses and prisms are now type-changing.
More informative error messages
More readable type signatures in type errors and when using :t
Use doctest
Include examples in Haddock
Breaking API changes
The type parameters of the classes have been changed to accommodate
the type-changing update:
class HasField name a s -> class HasField name s t a b etc.
Accordingly, field :: Lens' s a -> field :: Lens s t a b
