This module provides linear traversals.

Traversals provides a means of accessing several as organized in some structural way in an s, and a means of changing them to bs to create a t. In very ordinary language, it's like walking or traversing the data structure, going across cases and inside definitions. In more imaginative language, it's like selecting some specific as by looking at each constructor of a data definition and recursing on each non-basic type (where basic types are things like Int, Bool or Char).

Example

{-# LANGUAGE LinearTypes #-} {-# LANGUAGE NoImplicitPrelude #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE GADTs #-} import Control.Optics.Linear.Internal import qualified Control.Functor.Linear as Control import Control.Functor.Linear (($), (*), pure) import Prelude.Linear -- We can use a traversal to append a string only to the -- human names in a classroom struct appendToNames :: String -> Classroom %1-> Classroom appendToNames s = over classroomNamesTrav (name -> name ++ s) data Classroom where Classroom :: { className :: String , teacherName :: String , classNum :: Int , students :: [Student] , textbooks :: [String] } %1-> Classroom -- A Student is a name and a student id number data Student = Student String Int classroomNamesTrav :: Traversal' Classroom String classroomNamesTrav = traversal traverseClassStr where traverseClassStr :: forall f. Control.Applicative f => (String %1-> f String) -> Classroom %1-> f Classroom traverseClassStr onName (Classroom cname teachname x students texts) = Classroom $ pure cname * onName teachname * pure x * traverse' ((Student s i) -> Student $ onName s * pure i) students * pure texts