extensible-effects: An Alternative to Monad Transformers

[ control, effect, library, mit ] [ Propose Tags ]

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 [faq] 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), transformers (>=0.3 && <0.5), transformers-base (==0.4.*) [details]
License MIT
Author Oleg Kiselyov, Amr Sabry, Cameron Swords, Ben Foppa
Maintainer suhailshergill@gmail.com
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 Wed Nov 19 03:00:46 UTC 2014
Distributions NixOS:5.0.0.1
Downloads 13858 total (612 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by rule of succession]
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Readme for extensible-effects-1.7.1.2

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

Advantages

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

Disadvantages

  • 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.

  • 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.