reflection: Functional Pearl: Implicit Configurations

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

This package provides an implementation of the ideas presented in the paper "Functional Pearl: Implicit Configurations" by Oleg Kiselyov and Chung-chieh Shan. However, the API has been modified to use TypeFamilies and the implementation has been streamlined to improve performance.

The original paper can be obtained from

Changes in 1.0:

  • Much faster implementation available that is about 50 times faster than 0.9 and which runs purely on black magic. This version is now used by default. To turn it off install with the slow flag. If you encounter a problem with implementation, please contact the author.

Changes in 0.9:

  • Faster internal implementation, about 40 percent faster than 0.8.

  • Removed ReifiedNum, reflectNum, and reifyIntegral; reify and reflect are considerably faster than the special case combinators were.

Changes in 0.8:

  • Switched to using type families to avoid a problem where the user could cast Proxy (s a) -> Proxy (s b) and get back a values with the wrong type under the API in effect from 0.6. This API yields a much nicer example as well.

  • Removed reflectT as it no longer makes sense.

  • Added a more advanced example example/Constraints.hs using constraint kinds.

Changes in 0.7:

  • Uses a much simpler construction where reify now converts a StablePtr to an IntPtr and reifies that directly as an integral type rather than serializing and storing the StablePtr as a list of bytes as proposed in the original paper.

  • Removed ReifiedStorable and ReifiedNums.

  • Since we have so many fewer classes now, Data.Reflection.Internal was merged back into Data.Reflection

Changes in 0.6:

  • Removed the dependency on multiparameter type classes, functional dependencies, and flexible instances, by making Reifies a single parameter type class in the same fashion as ReifiesStorable.

  • Moved the building blocks to Data.Reflection.Internal to reduce API clutter.

  • Added reflectT

Changes in 0.5:

  • Generalized the type signatures in reflect to allow you to pass any type with kind * -> * wrapped around the desired type as the phantom type argument rather than just a Proxy.

Changes in 0.4:

  • Converted from Data.Tagged to using Data.Proxy for reflection. This reduces the need for helper functions and scoped type variables in user code.

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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,,, 0.4.1,, 0.5,, 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,, 1.1.6, 1.1.7,, 1.3, 1.3.1, 1.3.2, 1.4, 1.5.1,,, 1.5.2,, 2, 2.1, 2.1.1,, 2.1.2, 2.1.3, 2.1.4, 2.1.5, 2.1.6, 2.1.7
Dependencies base (>=4 && <5), tagged (>=0.2.3 && <0.3) [details]
License BSD-3-Clause
Copyright 2009-2012 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 <>
Category Data, Reflection, Dependent Types
Home page
Source repo head: git clone git://
Uploaded by EdwardKmett at 2012-04-07T10:36:03Z
Distributions Arch:2.1.7, Debian:2.1.6, Fedora:2.1.6, FreeBSD:2, LTSHaskell:2.1.7, NixOS:2.1.7, Stackage:2.1.7, openSUSE:2.1.6
Reverse Dependencies 92 direct, 6736 indirect [details]
Downloads 210890 total (324 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by Bayesian average]
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Readme for reflection-1.0

[back to package description]

This package provides an implementation of the ideas presented in the paper

  Oleg Kiselyov and Chung-Chieh Shan, "Functional Pearl: Implicit Configurations"

However, the API has been modified to use Rank2Types and TypeFamilies and the
implementation has been streamlined to improve performance.