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name: lens
category: Data, Lenses
version: 3.5.1
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.
.
An overview, with a large number of examples can be found in the README.
.
<https://github.com/ekmett/lens#lens-lenses-folds-and-traversals>
.
More information on the care and feeding of lenses, including a brief 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:
.
<<http://i.imgur.com/keOs9.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 if 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, GHC == 7.6.1
extra-source-files:
.travis.yml
.ghci
.gitignore
.vim.custom
config
examples/LICENSE
examples/lens-examples.cabal
examples/Pong.hs
examples/Plates.hs
examples/Aeson.hs
examples/Brainfuck.hs
examples/bf-examples/*.bf
README.markdown
CHANGELOG.markdown
source-repository head
type: git
location: git://github.com/ekmett/lens.git
-- Enable benchmarking against Neil Mitchell's uniplate library for comparative performance analysis. Defaults to being turned off to avoid
-- the extra dependency.
--
-- > cabal configure --enable-benchmarks -fbenchmark-uniplate && cabal build && cabal bench
flag benchmark-uniplate
default: False
manual: True
-- Enable template haskell. Disable this at your own risk and for testing only.
--
-- cabal configure -f-template-haskell is an /unsuppported/ configuration.
--
-- Clients of this library can and should expect this to be turned on.
flag template-haskell
default: True
manual: True
-- Generate inline pragmas when using template-haskell. This defaults to enabled, but you can
--
-- > cabal install lens -f-inlining
--
-- to shut it off to benchmark the relative performance impact, or as last ditch effort to address compile
-- errors resulting from the myriad versions of template-haskell that all purport to be 2.8.
flag inlining
manual: True
default: True
-- Some 7.6.1-rc1 users report their TH still uses old style inline pragmas. This lets them turn on inlining.
flag old-inline-pragmas
default: False
manual: True
-- Make the test suites dump their template-haskell splices.
flag dump-splices
default: False
manual: True
library
build-depends:
base >= 4.4 && < 5,
bytestring >= 0.9.1.10 && < 0.11,
comonad == 3.0.*,
comonad-transformers == 3.0.*,
comonads-fd == 3.0.*,
containers >= 0.4.2 && < 0.6,
hashable == 1.1.*,
mtl >= 2.1.1 && < 2.2,
semigroups >= 0.8.4 && < 0.9,
split == 0.2.*,
text >= 0.11 && < 0.12,
transformers >= 0.3 && < 0.4,
unordered-containers >= 0.2 && < 0.3,
vector >= 0.9 && < 0.11
exposed-modules:
Control.Exception.Lens
Control.Lens
Control.Lens.Action
Control.Lens.Classes
Control.Lens.Combinators
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.Isomorphic
Control.Lens.Loupe
Control.Lens.Plated
Control.Lens.Projection
Control.Lens.Representable
Control.Lens.Setter
Control.Lens.Simple
Control.Lens.Traversal
Control.Lens.Tuple
Control.Lens.Type
Control.Lens.Unsafe
Control.Lens.WithIndex
Control.Lens.Zipper
Control.Lens.Zoom
Data.Bits.Lens
Data.ByteString.Lens
Data.ByteString.Strict.Lens
Data.ByteString.Lazy.Lens
Data.Complex.Lens
Data.Data.Lens
Data.Dynamic.Lens
Data.HashSet.Lens
Data.IntSet.Lens
Data.List.Lens
Data.List.Split.Lens
Data.Monoid.Lens
Data.Sequence.Lens
Data.Set.Lens
Data.Text.Lens
Data.Text.Strict.Lens
Data.Text.Lazy.Lens
Data.Tree.Lens
Data.Typeable.Lens
Data.Vector.Lens
Data.Vector.Generic.Lens
other-modules:
Control.Lens.Internal.BazaarT
Control.Lens.Internal.Combinators
if flag(template-haskell)
build-depends: template-haskell >= 2.4 && < 2.9
exposed-modules: Control.Lens.TH Language.Haskell.TH.Lens
else
cpp-options: -DDISABLE_TEMPLATE_HASKELL
-- platform
build-depends: array >= 0.3.0.2 && < 0.5
exposed-modules: Data.Array.Lens
build-depends: filepath >= 1.2.0.0 && < 1.4
exposed-modules: System.FilePath.Lens
build-depends: parallel >= 3.1.0.1 && < 3.3
exposed-modules: Control.Parallel.Strategies.Lens Control.Seq.Lens
if impl(ghc>=7.6.0.20120810)
if flag(old-inline-pragmas)
cpp-options: -DOLD_INLINE_PRAGMAS
if !flag(inlining)
cpp-options: -DOMIT_INLINING
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 that Template Haskell expansion works
test-suite templates
type: exitcode-stdio-1.0
main-is: templates.hs
build-depends:
base,
lens
ghc-options: -Wall -threaded
if flag(dump-splices)
ghc-options: -ddump-splices
if impl(ghc<7.6.1)
ghc-options: -Werror
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,
lens,
QuickCheck >= 2.4 && < 2.6,
transformers
ghc-options: -w -threaded
hs-source-dirs: tests
test-suite hunit
type: exitcode-stdio-1.0
main-is: hunit.hs
build-depends:
base,
containers,
HUnit == 1.2.*,
lens,
mtl,
test-framework == 0.6.*,
test-framework-hunit == 0.2.*,
test-framework-th == 0.2.*
ghc-options: -w -threaded
hs-source-dirs: tests
-- Verify the results of the examples
test-suite doctests
type: exitcode-stdio-1.0
main-is: doctests.hs
build-depends:
base,
directory >= 1.0 && < 1.3,
doctest >= 0.9.1 && <= 0.10,
filepath
ghc-options: -Wall -threaded
if impl(ghc<7.6.1)
ghc-options: -Werror
hs-source-dirs: tests
-- Basic benchmarks for the uniplate-style combinators
benchmark plated
type: exitcode-stdio-1.0
main-is: plated.hs
build-depends:
base,
comonad,
criterion,
deepseq,
ghc-prim,
lens,
transformers
ghc-options: -Wall -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
if flag(benchmark-uniplate)
build-depends: uniplate >= 1.6.7 && < 1.7
cpp-options: -DBENCHMARK_UNIPLATE
-- Basic benchmarks for the uniplate-style combinators
benchmark alongside
type: exitcode-stdio-1.0
main-is: alongside.hs
build-depends:
base,
comonad,
comonads-fd,
criterion,
deepseq,
ghc-prim,
lens,
transformers
ghc-options: -w -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
-- Basic benchmarks for the uniplate-style combinators
benchmark unsafe
type: exitcode-stdio-1.0
main-is: unsafe.hs
build-depends:
base,
comonad,
comonads-fd,
criterion,
deepseq,
ghc-prim,
lens,
transformers
ghc-options: -w -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
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