extensible-effects: An Alternative to Monad Transformers

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This package introduces datatypes for typeclass-constrained effects, as an alternative to monad-transformer based (datatype-constrained) approach of multi-layered effects. For more information, see the original paper at http://okmij.org/ftp/Haskell/extensible/exteff.pdf. Any help is appreciated!

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Versions	1.0, 1.1.0, 1.2.0, 1.2.1, 1.4.1, 1.5.0, 1.6.0, 1.7.1, 1.7.1.0, 1.7.1.1, 1.7.1.2, 1.7.2.1, 1.8.0.0, 1.8.1.0, 1.9.0.0, 1.9.0.1, 1.9.1.0, 1.9.2.2, 1.10.0.1, 1.11.0.0, 1.11.0.1, 1.11.0.2, 1.11.0.3, 1.11.0.4, 1.11.1.0, 2.0.0.0, 2.0.0.2, 2.0.1.0, 2.0.1.0, 2.1.0.0, 2.2.1.0, 2.3.0.0, 2.3.0.1, 2.4.0.0, 2.5.0.0, 2.5.1.0, 2.5.1.2, 2.5.2.0, 2.5.3.0, 2.6.0.0, 2.6.0.1, 2.6.0.2, 2.6.0.3, 2.6.1.0, 2.6.1.1, 2.6.2.0, 2.6.3.0, 3.0.0.0, 3.1.0.0, 3.1.0.1, 3.1.0.2, 4.0.0.0, 5.0.0.0, 5.0.0.1
Change log	None available
Dependencies	base (>=4.6 && <5), transformers (>=0.3 && <0.6), transformers-base (>=0.4 && <0.5), type-aligned (>=0.9.3) [details]
License	MIT
Author	Oleg Kiselyov, Amr Sabry, Cameron Swords, Ben Foppa
Maintainer	suhailshergill@gmail.com
Category	Control, Effect
Home page	https://github.com/suhailshergill/extensible-effects
Source repo	head: git clone https://github.com/suhailshergill/extensible-effects.git
Uploaded	by shergill at 2017-11-20T02:38:23Z

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force-openunion-51	Force usage of OpenUnion51.hs implementation	Enabled

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extensible-effects-2.0.1.0.tar.gz [browse] (Cabal source package)
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BenFoppa, SvenHeyll, shergill, sickmind

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Readme for extensible-effects-2.0.1.0

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extensible-effects is based on the work Extensible Effects: An Alternative to Monad Transformers. Please read the paper and the followup freer paper for details. Additional explanation behind the approach can be found on Oleg's website.

[![Join the chat at https://gitter.im/suhailshergill/extensible-effects](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/suhailshergill/extensible-effects?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)

Advantages

Effects can be added, removed, and interwoven without changes to code not dealing with those effects.

Disadvantages

Current implementation only supports GHC version 7.8 and above

Ambiguity-Flexibility tradeoff

The extensibility comes at the cost of some ambiguity. Note, however, that the extensibility can be traded back, but that detracts from some of the advantages. For details see section 4.1 in the paper. This issue manifests itself in a few ways:
- Common functions can't be grouped using typeclasses, e.g. the ask and getState functions can't be grouped with some
```
class Get t a where
  ask :: Member (t a) r => Eff r a
```
  ask is inherently ambiguous, since the type signature only provides a constraint on t, and nothing more. To specify fully, a parameter involving the type t would need to be added, which would defeat the point of having the grouping in the first place.
- Code requires greater number of type annotations. For details see #31.