@hackage extensible-effects1.9.1.0

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

[](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

For GHC version 7.8 and upwards

• 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.

  • fixed by https://github.com/suhailshergill/extensible-effects/issues/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 https://github.com/suhailshergill/extensible-effects/issues/38