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 [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 && <4.9), transformers (>=0.3 && <0.6), transformers-base (>=0.4 && <0.5), type-aligned (>=0.9.3), void (>=0.6 && <0.8) [details]
License MIT
Author Oleg Kiselyov, Amr Sabry, Cameron Swords, Ben Foppa
Maintainer suhailshergill@gmail.com
Revised Revision 1 made by AdamBergmark at 2016-06-04T16:06:31Z
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 2016-01-24T23:27:13Z
Distributions LTSHaskell:5.0.0.1, NixOS:5.0.0.1, Stackage:5.0.0.1
Reverse Dependencies 12 direct, 0 indirect [details]
Downloads 35607 total (137 in the last 30 days)
Rating 2.25 (votes: 2) [estimated by Bayesian average]
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Status Docs available [build log]
Last success reported on 2016-01-24 [all 1 reports]

Readme for extensible-effects-1.11.0.2

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

Build Status Join the chat at https://gitter.im/suhailshergill/extensible-effects

Advantages

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

Disadvantages

For GHC version 7.8 and upwards

  • 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.

  • Requires a Typeable instance on the return type. This is no longer a limitation on GHC versions 7.8 and above.
    • fixed by #38.

For GHC versions prior to 7.8

  • 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.
    • fixed by #38.