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name: lens
category: Data, Lenses
version: 3.8.7
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) 2012-2013 Edward A. Kmett
build-type: Custom
tested-with: GHC == 7.0.4, GHC == 7.4.1, GHC == 7.4.2, GHC == 7.6.1, GHC == 7.7.20121213, GHC == 7.7.20130117
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>
.
A video on how to use lenses and how they are constructed is available from youtube: <http://youtu.be/cefnmjtAolY?hd=1>
.
Slides can be obtained here: <http://comonad.com/haskell/Lenses-Folds-and-Traversals-NYC.pdf>
.
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 of @pong@ and other more complex examples that manage their state using lenses can be found in the example folder: <https://github.com/ekmett/lens/blob/master/examples/>
.
/Lenses, Folds and Traversals/
.
The core of the hierarchy of lens-like constructions looks like:
.
<<http://i.imgur.com/RFi75.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 linked 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 :: 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 :: 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).
extra-source-files:
.travis.yml
.ghci
.gitignore
.vim.custom
examples/LICENSE
examples/lens-examples.cabal
examples/*.hs
examples/*.lhs
examples/bf-examples/*.bf
travis/cabal-apt-install
travis/config
AUTHORS.markdown
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
-- 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
-- You can disable the doctests test suite with -f-test-doctests
flag test-doctests
default: True
manual: True
-- You can disable the hunit test suite with -f-test-hunit
flag test-hunit
default: True
manual: True
-- Build the properties test if we're building tests
flag test-properties
default: True
manual: True
-- Disallow unsafeCoerce
flag safe
default: False
manual: True
-- Assert that we are trustworthy when we can
flag trustworthy
default: True
manual: True
flag lib-Werror
default: False
manual: True
library
build-depends:
array >= 0.3.0.2 && < 0.5,
base >= 4.3 && < 5,
bifunctors >= 3 && < 4,
bytestring >= 0.9.1.10 && < 0.11,
comonad >= 3 && < 4,
comonad-transformers >= 3 && < 4,
comonads-fd >= 3 && < 4,
contravariant >= 0.2.0.2 && < 1,
containers >= 0.4.0 && < 0.6,
distributive >= 0.3 && < 1,
filepath >= 1.2.0.0 && < 1.4,
generic-deriving == 1.4.*,
ghc-prim,
hashable >= 1.1.2.3 && < 1.3,
MonadCatchIO-transformers >= 0.3 && < 0.4,
mtl >= 2.0.1 && < 2.2,
parallel >= 3.1.0.1 && < 3.3,
profunctors >= 3.2 && < 4,
profunctor-extras >= 3.3 && < 4,
reflection >= 1.1.6 && < 2,
semigroupoids >= 3 && < 4,
semigroups >= 0.8.4 && < 1,
split == 0.2.*,
tagged >= 0.4.4 && < 1,
template-haskell >= 2.4 && < 2.10,
text >= 0.11 && < 0.12,
transformers >= 0.2 && < 0.4,
transformers-compat >= 0.1 && < 1,
unordered-containers >= 0.2 && < 0.3,
vector >= 0.9 && < 0.11,
void >= 0.5 && < 1
exposed-modules:
Control.Exception.Lens
Control.Lens
Control.Lens.Action
Control.Lens.At
Control.Lens.Combinators
Control.Lens.Cons
Control.Lens.Each
Control.Lens.Equality
Control.Lens.Fold
Control.Lens.Getter
Control.Lens.Indexed
Control.Lens.Internal
Control.Lens.Internal.Action
Control.Lens.Internal.Bazaar
Control.Lens.Internal.ByteString
Control.Lens.Internal.Context
Control.Lens.Internal.Deque
Control.Lens.Internal.Exception
Control.Lens.Internal.Fold
Control.Lens.Internal.Getter
Control.Lens.Internal.Indexed
Control.Lens.Internal.Instances
Control.Lens.Internal.Iso
Control.Lens.Internal.Level
Control.Lens.Internal.Magma
Control.Lens.Internal.Prism
Control.Lens.Internal.Review
Control.Lens.Internal.Setter
Control.Lens.Internal.Zipper
Control.Lens.Internal.Zoom
Control.Lens.Iso
Control.Lens.Lens
Control.Lens.Level
Control.Lens.Loupe
Control.Lens.Operators
Control.Lens.Plated
Control.Lens.Prism
Control.Lens.Reified
Control.Lens.Review
Control.Lens.Setter
Control.Lens.Simple
Control.Lens.TH
Control.Lens.Traversal
Control.Lens.Tuple
Control.Lens.Type
Control.Lens.Wrapped
Control.Lens.Zipper
Control.Lens.Zoom
Control.Monad.Error.Lens
Control.Parallel.Strategies.Lens
Control.Seq.Lens
Data.Array.Lens
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.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
Generics.Deriving.Lens
GHC.Generics.Lens
System.Exit.Lens
System.FilePath.Lens
System.IO.Error.Lens
Language.Haskell.TH.Lens
Numeric.Lens
if flag(safe)
cpp-options: -DSAFE=1
if flag(trustworthy) && impl(ghc>=7.2)
other-extensions: Trustworthy
cpp-options: -DTRUSTWORTHY=1
if flag(old-inline-pragmas) && impl(ghc>=7.6.0.20120810)
cpp-options: -DOLD_INLINE_PRAGMAS=1
if flag(inlining)
cpp-options: -DINLINING
if flag(lib-Werror)
ghc-options: -Werror
if impl(ghc<7.4)
ghc-options: -fno-spec-constr-count
if impl(ghc>=7.2)
cpp-options: -DDEFAULT_SIGNATURES=1
ghc-options: -Wall -fwarn-tabs -O2 -fdicts-cheap -funbox-strict-fields -fmax-simplifier-iterations=10
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
hs-source-dirs: tests
if flag(dump-splices)
ghc-options: -ddump-splices
if impl(ghc<7.6.1)
ghc-options: -Werror
-- Verify the properties of lenses with QuickCheck
test-suite properties
type: exitcode-stdio-1.0
main-is: properties.hs
ghc-options: -w -threaded -rtsopts -with-rtsopts=-N
hs-source-dirs: tests
if !flag(test-properties)
buildable: False
else
build-depends:
base,
lens,
QuickCheck >= 2.4,
test-framework >= 0.6,
test-framework-quickcheck2 >= 0.2,
test-framework-th >= 0.2,
transformers
test-suite hunit
type: exitcode-stdio-1.0
main-is: hunit.hs
ghc-options: -w -threaded -rtsopts -with-rtsopts=-N
hs-source-dirs: tests
if !flag(test-hunit)
buildable: False
else
build-depends:
base,
containers,
HUnit >= 1.2,
lens,
mtl,
test-framework >= 0.6,
test-framework-hunit >= 0.2,
test-framework-th >= 0.2
-- Verify the results of the examples
test-suite doctests
type: exitcode-stdio-1.0
main-is: doctests.hs
ghc-options: -Wall -threaded
hs-source-dirs: tests
if !flag(test-doctests)
buildable: False
else
build-depends:
base,
bytestring,
containers,
directory >= 1.0,
deepseq,
doctest >= 0.9.1,
filepath,
generic-deriving,
mtl,
nats,
parallel,
semigroups >= 0.9,
simple-reflect >= 0.3.1,
split,
text,
unordered-containers,
vector
if impl(ghc<7.6.1)
ghc-options: -Werror
-- Basic benchmarks for the uniplate-style combinators
benchmark plated
type: exitcode-stdio-1.0
main-is: plated.hs
ghc-options: -Wall -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
build-depends:
base,
comonad,
criterion,
deepseq,
generic-deriving,
lens,
transformers
if flag(benchmark-uniplate)
build-depends: uniplate >= 1.6.7 && < 1.7
cpp-options: -DBENCHMARK_UNIPLATE
-- Benchmarking alongside variants
benchmark alongside
type: exitcode-stdio-1.0
main-is: alongside.hs
ghc-options: -w -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
build-depends:
base,
comonad,
comonads-fd,
criterion,
deepseq,
lens,
transformers
-- Benchmarking unsafe implementation strategies
benchmark unsafe
type: exitcode-stdio-1.0
main-is: unsafe.hs
ghc-options: -w -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
build-depends:
base,
comonad,
comonads-fd,
criterion,
deepseq,
generic-deriving,
lens,
transformers
-- Benchmarking zipper usage
benchmark zipper
type: exitcode-stdio-1.0
main-is: zipper.hs
ghc-options: -w -O2 -threaded -fdicts-cheap -funbox-strict-fields
hs-source-dirs: benchmarks
build-depends:
base,
comonad,
comonads-fd,
criterion,
deepseq,
generic-deriving,
lens,
transformers
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