references-0.2.1.2: references.cabal
name: references
version: 0.2.1.2
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: <https://hackage.haskell.org/package/lens>).
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There are two things that references can do but the previously mentioned access methods don't.
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* References can cooperate with monads, for example IO.
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* References can be added using the @&+&@ operator, to create new lenses more easily.
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Basic idea taken from the currently not maintained package <https://hackage.haskell.org/package/yall>.
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An example use of the references (a logger application that spawns new threads to update a global log):
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> 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
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There are a bunch of predefined references for datatypes included in standard libraries.
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New references can be created in several ways:
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* From getter, setter and updater, using the @reference@ function.
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* From getter and setter, using one of the simplified functions (@lens@, @simplePartial@, @partial@, ...).
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* Using the `Data.Traversal` instance on a datatype to generate a traversal of each element.
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* 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.
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* Generating references for newly defined records using the `makeReferences` Template Haskell function.
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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.Predefined.Containers
, Control.Reference.Predefined.Containers.Tree
, Control.Reference.TupleInstances
, Control.Reference.InternalInterface
build-depends: base >=4.6 && <5
, text ==1.1.*
, array ==0.5.*
, 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