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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. Labels can be used to get, set and modify parts of a datatype in a consistent way. See Data.Label for an introductory explanation. Internally lenses are not tied to Haskell functions directly, but are implemented as arrows. Arrows 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. See the Data.Label.Maybe module for the use of partial labels.