The extensible-effects package

[ Tags: 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 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 (info)
Dependencies base (>=4.6 && <5), transformers (>=0.3 && <0.6), transformers-base (==0.4.*), 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 repository head: git clone https://github.com/suhailshergill/extensible-effects.git
Uploaded Mon Nov 20 02:39:18 UTC 2017 by shergill
Distributions LTSHaskell:1.11.1.0, NixOS:2.0.1.0, Stackage:2.0.1.0, Tumbleweed:1.11.1.0
Downloads 5560 total (175 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by rule of succession]
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Status Docs available [build log]
Last success reported on 2017-11-20 [all 1 reports]
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Modules

[Index]

Flags

NameDescriptionDefaultType
lib-werrorDisabledManual
force-openunion-51

Force usage of OpenUnion51.hs implementation

EnabledManual

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

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Maintainer's Corner

For package maintainers and hackage trustees


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.

Build Status Join the chat at <a href="https://gitter.im/suhailshergill/extensible-effects">https://gitter.im/suhailshergill/extensible-effects</a> Stories in Ready Stories in progress

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.