@hackage extensible-effects1.8.1.0

An Alternative to Monad Transformers

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

Build Status

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. 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.