extensible-effects: An Alternative to Monad Transformers

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 [RSS]	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, 2.1.0.0, 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 (info)
Dependencies	base (>=4.6 && <5), free (>=4.0 && <5.0), kan-extensions (>=4.0 && <5.0), transformers (>=0.3 && <0.5), transformers-base (>=0.4 && <0.5) [details]
Tested with	ghc ==7.8.3, ghc ==7.6.3
License	MIT
Author	Oleg Kiselyov, Amr Sabry, Cameron Swords, Ben Foppa
Maintainer	[email protected]
Category	Control, Effect
Home page	https://github.com/RobotGymnast/extensible-effects
Source repo	head: git clone https://github.com/RobotGymnast/extensible-effects.git
Uploaded	by shergill at 2014-12-11T11:49:39Z
Distributions	LTSHaskell:5.0.0.1, NixOS:5.0.0.1
Reverse Dependencies	12 direct, 0 indirect [details]
Downloads	37307 total (31 in the last 30 days)
Rating	2.25 (votes: 2) [estimated by Bayesian average]
Your Rating	λ λ λ
Status	Docs uploaded by user Build status unknown [no reports yet]

extensible-effects is based on the work Extensible Effects: An Alternative to Monad Transformers. Please read the paper for details.

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

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.
Requires a Typeable instance on the return type. This is no longer a limitation on GHC versions 7.8 and above.
Neither Eff nor (:>) has a Typeable instance, and can thus often not be used as a return type (e.g. State type) for other Effs. This is no longer a concern for GHC versions 7.8 and above.