This package provides first class labels that can act as bidirectional record fields. The labels can be derived automatically using Template Haskell which means you don't have to write any boilerplate yourself. The labels are implemented as lenses and are fully composable. Lenses can be used to get, set and modify parts of a data type in a consistent way.
Data.Label for an introductory explanation or see the
introductory blog post at
Total and partial lenses
Internally lenses do not used Haskell functions directly, but are implemented as categories. Categories allow the lenses to be run in custom computational contexts. This approach allows us to make partial lenses that point to fields of multi-constructor datatypes in an elegant way.
Data.Label.Partial for the use of partial labels.
Monomorphic and polymorphic lenses
We have both polymorphic and monomorphic lenses. Polymorphic lenses allow updates that change the type. The types of polymorphic lenses are slightly more verbose than their monomorphic counterparts, but their usage is similar. Because monomorphic lenses are built by restricting the types of polymorphic lenses they are essentially the same and can be freely composed with eachother.
Data.Label.Poly for the difference
between polymorphic and monomorphic lenses.
To simplify working with labels we supply both a set of labels for Haskell's base types, like lists, tuples, Maybe and Either, and we supply a set of combinators for working with labels for values in the Reader and State monad.
Data.Label.Monadic for more
Changelog from 184.108.40.206 to 220.127.116.11
- Restored support for GHC 7.4.