reflection: Reifies arbitrary terms into types that can be reflected back into terms

[ bsd3, data, dependent-types, library, reflection ] [ Propose Tags ]

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.


[Skip to Readme]

Modules

[Index]

Flags

Manual Flags

NameDescriptionDefault
thEnabled
Automatic Flags
NameDescriptionDefault
slowDisabled

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info

Downloads

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

Package maintainers

For package maintainers and hackage trustees

Candidates

  • No Candidates
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 2018-09-24T16:48:51Z
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 2015-01-22T06:38:40Z
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 215193 total (461 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by Bayesian average]
Your Rating
  • λ
  • λ
  • λ
Status Docs available [build log]
Last success reported on 2015-01-22 [all 1 reports]

Readme for reflection-1.5.1.1

[back to package description]

reflection

Build Status

This package provides an implementation of the ideas presented in Functional Pearl: Implicit Configurations by Oleg Kiselyov and Chung-Chieh Shan. However, the API has been implemented in a much more efficient manner.

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the #haskell IRC channel on irc.freenode.net.

-Edward Kmett