Copyright	(C) 2016 Aaron Levin
License	BSD-style (see the file LICENSE)
Maintainer	Aaron Levin <aaron.michael.benjamin.levin@gmail.com>
Stability	provisional
Portability	non-portable (rank-2 polymorphism)
Safe Haskell	None
Language	Haskell2010

Control.Monad.Free.VanLaarhovenE

Description

"van Laarhoven encoded Free Monad with extensible effects"

Synopsis

Documentation

(.:.) :: effect m -> Effects effects m -> Effects (effect : effects) m infixr 4 Source

Helper combinator for creating values of 'Effects effects m'

data Effects a m where Source

a customized HList of effects. We need to carry the m param around for type inference.

Constructors

EmptyE :: Effects `[]` m
ConsE :: effect m -> Effects effects m -> Effects (effect : effects) m

newtype Free effects a Source

The van Laarhoven-encoded Free Monad with Extensible effects

Constructors

Free
Fields runFree :: forall m. Monad m => Effects effects m -> m a

Instances

Monad (Free effect) Source
Functor (Free effect) Source
Applicative (Free effect) Source

class HasEffect effects effect where Source

A class to help us fetch effects from our effect stack.

Methods

getEffect :: Effects effects m -> effect m Source

Instances

HasEffect ((:) ((* -> ) -> ) effect effects) effect Source	An instance of `HasEffect` that handles the case where our desired effect type matches the head of the list. We then return that effect.
HasEffect effects effect => HasEffect ((:) ((* -> ) -> ) notIt effects) effect Source	An instance of `HasEffect` that handles the case where our desired effect type doesn't match the head of the HList.

iterM :: Monad m => Effects effects m -> Free effects a -> m a Source

Tear down a Free Monad using the supplied effects value.

liftF :: HasEffect effects effect => (forall m. Monad m => effect m -> m a) -> Free effects a Source

A version of lift that can be used with an effect stack.