name: references version: 0.2.1.1 x-revision: 1 synopsis: Generalization of lenses, folds and traversals to handle monads and addition. description: References can read, write or update parts of the data. They are first-class values, can be passed in functions, transformed, combined. References generalize lenses, folds and traversals for haskell (see: ). . There are two things that references can do but the previously mentioned access methods don't. . * References can cooperate with monads, for example IO. . * References can be added using the @&+&@ operator, to create new lenses more easily. . Basic idea taken from the currently not maintained package . . An example use of the references (a logger application that spawns new threads to update a global log): . > logger = > (forever $ do > log <- logChan ^! chan&logRecord -- Extract the log record from the received log message > thrId <- forkIO (do time <- getTime > ioref&lastLogTime != time $ logDB -- Update the last logging time mutable log database > let logMsg = senderThread .- show -- Transform the thread id to a string and > $ loggingTime .= time -- update the time > $ log -- inside the log message > ioref&debugInfos !~ addLogEntry log $ logDB -- update the table of log entries > mvar !- (+1) $ count ) > mvar !- (thrId:) $ updaters -- Record the spawned thread > ) `catch` stopUpdaters updaters > where stopUpdaters updaters ThreadKilled = > mvar&traverse *!| killThread $ updaters -- Kill all spawned threads before stopping . There are a bunch of predefined references for datatypes included in standard libraries. . New references can be created in several ways: . * From getter, setter and updater, using the @reference@ function. . * From getter and setter, using one of the simplified functions (@lens@, @simplePartial@, @partial@, ...). . * Using the `Data.Traversal` instance on a datatype to generate a traversal of each element. . * Using lenses from `Control.Lens` package. There are a lot of packages defining lenses, folds and traversals for various data structures, so it is very useful that all of them can simply be converted into a reference. . * Generating references for newly defined records using the `makeReferences` Template Haskell function. . homepage: https://github.com/lazac/references license: BSD3 license-file: LICENSE author: Boldizsar Nemeth maintainer: nboldi@elte.hu -- copyright: category: Control build-type: Simple cabal-version: >=1.8 library exposed-modules: Control.Reference , Control.Reference.TH.MonadInstances , Control.Reference.TH.Monad , Control.Reference.TH.Records , Control.Reference.TH.Tuple , Control.Reference.Examples.TH , Control.Reference.Representation , Control.Reference.Operators , Control.Reference.Predefined , Control.Reference.TupleInstances , Control.Reference.InternalInterface build-depends: base >=4.6 && <5 , mtl ==2.2.* , transformers ==0.4.* , containers ==0.5.* , either ==4.3.* , template-haskell >=2.8 && <3 , transformers-base >= 0.4 && <0.5 , monad-control >= 0.3 && <0.4 , lifted-base >= 0.2 && <0.3