data-accessor: Utilities for accessing and manipulating fields of records
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.
The package data-accessor-template
provides Template Haskell functions
for automated generation of Data.Acesssor.Accessor
s.
Modules
[Index]
Downloads
- data-accessor-0.2.0.2.tar.gz [browse] (Cabal source package)
- Package description (as included in the package)
Maintainer's Corner
For package maintainers and hackage trustees
Candidates
Versions [RSS] | 0.0.1, 0.1.1, 0.1.2, 0.1.3, 0.1.4, 0.2, 0.2.0.1, 0.2.0.2, 0.2.1, 0.2.1.2, 0.2.1.3, 0.2.1.4, 0.2.1.5, 0.2.1.6, 0.2.1.7, 0.2.1.8, 0.2.2, 0.2.2.1, 0.2.2.2, 0.2.2.3, 0.2.2.4, 0.2.2.5, 0.2.2.6, 0.2.2.7, 0.2.2.8, 0.2.3, 0.2.3.1 |
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Dependencies | array (>=0.1 && <1), base (>=1.0), containers (>=0.1 && <1), transformers (>=0.0.1 && <0.2) [details] |
Tested with | ghc ==6.4.1 && ==6.8.2 |
License | BSD-3-Clause |
Author | Henning Thielemann <haskell@henning-thielemann.de>, Luke Palmer <lrpalmer@gmail.com> |
Maintainer | Henning Thielemann <haskell@henning-thielemann.de> |
Category | Data |
Home page | http://www.haskell.org/haskellwiki/Record_access |
Uploaded | by HenningThielemann at 2009-01-10T22:32:40Z |
Distributions | Arch:0.2.3.1, Debian:0.2.3, Fedora:0.2.3.1, LTSHaskell:0.2.3.1, NixOS:0.2.3.1, Stackage:0.2.3.1 |
Reverse Dependencies | 62 direct, 3710 indirect [details] |
Downloads | 52529 total (166 in the last 30 days) |
Rating | (no votes yet) [estimated by Bayesian average] |
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Status | Docs uploaded by user Build status unknown [no reports yet] |