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name: lens
category: Data, Lenses
version: 2.1
license: BSD3
cabal-version: >= 1.8
license-file: LICENSE
author: Edward A. Kmett
maintainer: Edward A. Kmett <ekmett@gmail.com>
stability: provisional
homepage: http://github.com/ekmett/lens/
bug-reports: http://github.com/ekmett/lens/issues
copyright: Copyright (C) 2012 Edward A. Kmett
synopsis: Lenses, Folds and Traversals
description:
This package comes \"Batteries Included\" with many useful lenses for the types
commonly used from the Haskell Platform, and with tools for automatically
generating lenses and isomorphisms for user-supplied data types.
.
The combinators in @Control.Lens@ provide a highly generic toolbox for composing
families of getters, folds, isomorphisms, traversals, setters and lenses and their
indexed variants.
.
More information on the care and feeding of lenses, including a tutorial and motivation
for their types can be found on the lens wiki.
.
<https://github.com/ekmett/lens/wiki>
.
A small game that manages its state using lenses can be found in the example folder.
.
<https://github.com/ekmett/lens/blob/master/examples/Pong.hs>
.
/Lenses, Folds and Traversals/
.
The core of this hierarchy looks like:
.
<<https://github.com/ekmett/lens/wiki/images/Hierarchy-2.1.png>>
.
You can compose any two elements of the hierarchy above using (.) from the Prelude, and you can
use any element of the hierarchy as any type it links to above it.
.
The result is their lowest upper bound in the hierarchy (or an error f that bound doesn't exist).
.
For instance:
.
* You can use any 'Traversal' as a 'Fold' or as a 'Setter'.
.
* The composition of a 'Traversal' and a 'Getter' yields a 'Fold'.
.
/Minimizing Dependencies/
.
If you want to provide lenses and traversals for your own types in your own libraries, then you
can do so without incurring a dependency on this (or any other) lens package at all.
.
e.g. for a data type:
.
> data Foo a = Foo Int Int a
.
You can define lenses such as
.
> -- bar :: Simple Lens (Foo a) Int
> bar :: Functor f => (Int -> f Int) -> Foo a -> f Foo a
> bar f (Foo a b c) = fmap (\a' -> Foo a' b c) (f a)
.
> -- baz :: Lens (Foo a) (Foo b) a b
> quux :: Functor f => (a -> f b) -> Foo a -> f (Foo b)
> quux f (Foo a b c) = fmap (Foo a b) (f c)
.
without the need to use any type that isn't already defined in the @Prelude@.
.
And you can define a traversal of multiple fields with 'Control.Applicative.Applicative':
.
> -- traverseBarAndBaz :: Simple Traversal (Foo a) Int
> traverseBarAndBaz :: Applicative f => (Int -> f Int) -> Foo a -> f (Foo a)
> traverseBarAndBaz f (Foo a b c) = Foo <$> f a <*> f b <*> pure c
.
What is provided in this library is a number of stock lenses and traversals for
common haskell types, a wide array of combinators for working them, and more
exotic functionality, (e.g. getters, setters, indexed folds, isomorphisms).
build-type: Simple
tested-with: GHC == 7.4.1
extra-source-files:
.travis.yml
.ghci
.gitignore
.vim.custom
config
examples/LICENSE
examples/lens-examples.cabal
examples/pong.hs
README.markdown
CHANGELOG.markdown
source-repository head
type: git
location: git://github.com/ekmett/lens.git
library
build-depends:
base >= 4.3 && < 5,
containers >= 0.4.2 && < 0.6,
mtl >= 2.1.1 && < 2.2,
template-haskell >= 2.4 && < 2.8,
transformers >= 0.3 && < 0.4
exposed-modules: Control.Exception.Lens
Control.Lens
Control.Lens.Action
Control.Lens.Fold
Control.Lens.Getter
Control.Lens.Indexed
Control.Lens.IndexedGetter
Control.Lens.IndexedFold
Control.Lens.IndexedLens
Control.Lens.IndexedSetter
Control.Lens.IndexedTraversal
Control.Lens.Internal
Control.Lens.Iso
Control.Lens.Representable
Control.Lens.Setter
Control.Lens.TH
Control.Lens.Traversal
Control.Lens.Type
Data.Bits.Lens
Data.Complex.Lens
Data.Dynamic.Lens
Data.Either.Lens
Data.List.Lens
Data.Pair.Lens
Data.IntMap.Lens
Data.IntSet.Lens
Data.Map.Lens
Data.Monoid.Lens
Data.Sequence.Lens
Data.Set.Lens
Data.Tree.Lens
Language.Haskell.TH.Lens
-- platform
build-depends: array >= 0.3.0.2 && < 0.5
exposed-modules: Data.Array.Lens
build-depends: bytestring >= 0.9.1.10 && < 0.10
exposed-modules: Data.ByteString.Lens Data.ByteString.Lazy.Lens
build-depends: text >= 0.11.1.5 && < 0.12
exposed-modules: Data.Text.Lens Data.Text.Lazy.Lens
build-depends: parallel >= 3.1.0.1 && < 3.3
exposed-modules: Control.Parallel.Strategies.Lens Control.Seq.Lens
other-extensions:
BangPatterns
CPP
DeriveDataTypeable
FlexibleContexts
FlexibleInstances
FunctionalDependencies
LiberalTypeSynonyms
MultiParamTypeClasses
Rank2Types
RankNTypes
TemplateHaskell
TypeFamilies
TypeOperators
UndecidableInstances
if (impl(ghc>=7.4))
other-extensions: Trustworthy
build-depends: ghc-prim
exposed-modules: GHC.Generics.Lens
ghc-options: -Wall -fwarn-tabs -O2 -fdicts-cheap -funbox-strict-fields
hs-source-dirs: src
-- Verify the results of the examples
test-suite doctests
type: exitcode-stdio-1.0
main-is: doctests.hs
build-depends:
base == 4.*,
directory >= 1.0 && < 1.2,
doctest >= 0.8 && <= 0.9,
filepath >= 1.3 && < 1.4
ghc-options: -Wall -Werror -threaded
hs-source-dirs: tests
-- Verify that Template Haskell expansion works
test-suite templates
type: exitcode-stdio-1.0
main-is: templates.hs
build-depends:
base == 4.*,
lens
ghc-options: -Wall -Werror -threaded
hs-source-dirs: tests
-- Verify the properties of lenses with QuickCheck
test-suite properties
type: exitcode-stdio-1.0
main-is: properties.hs
build-depends:
base == 4.*,
lens,
QuickCheck >= 2.4 && < 2.6,
transformers >= 0.3 && < 0.5
ghc-options: -w -threaded
hs-source-dirs: tests
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