dev-haskell / data-accessor

Utilities for accessing and manipulating fields of records

Official package sites : http://www.haskell.org/haskellwiki/Record_access ·

In Haskell 98 the name of a record field is automatically also the name of a function which gets the value of the according field. E.g. if we have data Pair a b = Pair first :: a, second :: b then > first :: Pair a b -> a > second :: Pair a b -> b However for setting or modifying a field value we need to use some syntactic sugar, which is often clumsy. modifyFirst :: (a -> a) -> (Pair a b -> Pair a b) modifyFirst f r\@(Pair first=a ) = r first = f a With this package you can define record field accessors which allow setting, getting and modifying values easily. The package clearly demonstrates the power of the functional approach: You can combine accessors of a record and sub-records, to make the access look like the fields of the sub-record belong to the main record. Example: > *Data.Accessor.Example> (first^:second^=10) (('b',7),"hallo") > (('b',10),"hallo") You can easily manipulate record fields in a 'Control.Monad.State.State' monad, you can easily code 'Show' instances that use the Accessor syntax and you can parse binary streams into records. See @Data.Accessor.Example@ for demonstration of all features. It would be great if in revised Haskell versions the names of record fields are automatically 'Data.Accessor.Accessor's rather than plain @get@ functions. For now, the package @data-accessor-template@ provides Template Haskell functions for automated generation of 'Data.Acesssor.Accessor's. See also the other @data-accessor@ packages that provide an Accessor interface to other data types. The package @enumset@ provides accessors to bit-packed records. For similar packages see @lenses@ and @fclabel@. A related concept are editors <http://conal.net/blog/posts/semantic-editor-combinators/>. Editors only consist of a modify method (and @modify@ applied to a 'const' function is a @set@ function). This way, they can modify all function values of a function at once, whereas an accessor can only change a single function value, say, it can change @f 0 = 1@ to @f 0 = 2@. This way, editors can even change the type of a record or a function. An Arrow instance can be defined for editors, but for accessors only a Category instance is possible ('(.)' method). The reason is the @arr@ method of the @Arrow@ class, that conflicts with the two-way nature (set and get) of accessors.

v0.2.2.7 :: 0/0.2.2.7 :: gentoo

Modified
License
BSD
Keywords
~amd64 ~x86
USE flags
doc hscolour profile

General

doc
Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
hscolour
Include coloured haskell sources to generated documentation (dev-haskell/hscolour)
profile
Add support for software performance analysis (will likely vary from ebuild to ebuild)

dev-haskell / cabal : A framework for packaging Haskell software

dev-haskell / haddock : A documentation-generation tool for Haskell libraries

dev-haskell / hscolour : Colourise Haskell code

dev-haskell / transformers : Concrete functor and monad transformers

dev-lang / ghc : The Glasgow Haskell Compiler

dev-haskell / transformers : Concrete functor and monad transformers

dev-lang / ghc : The Glasgow Haskell Compiler

dev-haskell / idiii : ID3v2 (tagging standard for MP3 files) library

Robin H. Johnson · gentoo
Drop $Id$ per council decision in bug #611234.
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Sergei Trofimovich · gentoo
dev-haskell/data-accessor: access library to record fields, a depend of dev-haskell/idiii
Package-Manager: portage-2.3.0