extensible-effects is based on the work
[Extensible Effects: An Alternative to Monad Transformers](http://okmij.org/ftp/Haskell/extensible/).
Please read the [paper](http://okmij.org/ftp/Haskell/extensible/exteff.pdf) and
the followup [freer paper](http://okmij.org/ftp/Haskell/extensible/more.pdf) for
details. Additional explanation behind the approach can be found on [Oleg's website](http://okmij.org/ftp/Haskell/extensible/).
[](https://travis-ci.org/suhailshergill/extensible-effects)
[](https://gitter.im/suhailshergill/extensible-effects?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
[](http://waffle.io/suhailshergill/extensible-effects)
[](http://waffle.io/suhailshergill/extensible-effects)
## 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](http://okmij.org/ftp/Haskell/extensible/exteff.pdf). 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](https://github.com/suhailshergill/extensible-effects/issues/31).