reflection: Reifies arbitrary terms into types that can be reflected back into terms
This package addresses the configuration problem which is
propogating configurations that are available at run-time, allowing
multible configurations to coexist without resorting to mutable
global variables or System.IO.Unsafe.unsafePerformIO
.
An example is modular arithmetic where the modulus itself can be supplied at run-time:
foo :: Modular s => Modulus s foo = 1000 * 1000 * 5 + 2000
>>>
withModulus 1280 foo
1040
given the following setup:
{-# LANGUAGE ScopedTypeVariables, RankNTypes, ConstraintKinds, FlexibleContexts, UndecidableInstances 125; import Data.Proxy (Proxy(Proxy)) import Data.Reflection (Reifies, reflect, reify)
and definitions:
data Modulus s = M { getModulus :: Integer } type Modular s =Data.Reflection.Reifies
s Integer normalize :: forall s. Modular s => Integer -> Modulus s normalize n = M (mod n modulus) where modulus =Data.Reflection.reflect
(Data.Proxy.Proxy
::Data.Proxy.Proxy
s) instance Modular s => Num (Modulus s) where M a + M b = normalize (a + b) M a * M b = normalize (a * b) withModulus :: Integer -> (forall s. Modular s => Modulus s) -> Integer withModulus m v =Data.Reflection.reify
m (getModulus . asProxyOf v) where asProxyOf :: f s -> Proxy s -> f s asProxyOf = const
That package is an implementation of the ideas presented in the paper "Functional Pearl: Implicit Configurations" by Oleg Kiselyov and Chung-chieh Shan (original paper). However, the API has been streamlined to improve performance.
Austin Seipp's tutorial Reflecting values to types and back provides a summary of the approach taken by this library, along with more motivating examples.
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Flags
Manual Flags
Name | Description | Default |
---|---|---|
template-haskell | You can disable the use of the `template-haskell` package using `-f-template-haskell`. Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users. | Enabled |
Automatic Flags
Name | Description | Default |
---|---|---|
slow | If you enable this flag, we use a more portable much much slower implementation. Moreover, the | Disabled |
Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info
Downloads
- reflection-1.5.2.tar.gz [browse] (Cabal source package)
- Package description (revised from the package)
Note: This package has metadata revisions in the cabal description newer than included in the tarball. To unpack the package including the revisions, use 'cabal get'.
Maintainer's Corner
For package maintainers and hackage trustees
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Versions [RSS] | 0.0.0, 0.1.0, 0.1.1, 0.2.0, 0.3.0, 0.3.1, 0.3.2, 0.3.3, 0.3.5, 0.4.0, 0.4.0.1, 0.4.0.2, 0.4.1, 0.4.1.1, 0.5, 0.5.0.1, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5, 1.1.5.1, 1.1.6, 1.1.7, 1.2.0.1, 1.3, 1.3.1, 1.3.2, 1.4, 1.5.1, 1.5.1.1, 1.5.1.2, 1.5.2, 1.5.2.1, 2, 2.1, 2.1.1, 2.1.1.1, 2.1.2, 2.1.3, 2.1.4, 2.1.5, 2.1.6, 2.1.7, 2.1.8 |
---|---|
Change log | CHANGELOG.markdown |
Dependencies | base (>=2 && <4.12), tagged (>=0.4.4 && <1), template-haskell [details] |
License | BSD-3-Clause |
Copyright | 2009-2013 Edward A. Kmett, 2012 Elliott Hird, 2004 Oleg Kiselyov and Chung-chieh Shan |
Author | Edward A. Kmett, Elliott Hird, Oleg Kiselyov and Chung-chieh Shan |
Maintainer | Edward A. Kmett <ekmett@gmail.com> |
Revised | Revision 1 made by phadej at 2018-09-24T16:48:52Z |
Category | Data, Reflection, Dependent Types |
Home page | http://github.com/ekmett/reflection |
Bug tracker | http://github.com/ekmett/reflection/issues |
Source repo | head: git clone git://github.com/ekmett/reflection.git |
Uploaded | by EdwardKmett at 2015-05-12T18:54:22Z |
Distributions | Arch:2.1.8, Debian:2.1.6, Fedora:2.1.7, FreeBSD:2, LTSHaskell:2.1.8, NixOS:2.1.8, Stackage:2.1.8, openSUSE:2.1.7 |
Reverse Dependencies | 94 direct, 7802 indirect [details] |
Downloads | 215158 total (453 in the last 30 days) |
Rating | 2.25 (votes: 2) [estimated by Bayesian average] |
Your Rating | |
Status | Docs available [build log] Last success reported on 2015-05-12 [all 1 reports] |