Control.Monad.Free.VanLaarhovenE

"van Laarhoven encoded Free Monad with extensible effects"

Documentation

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

Helper combinator for creating values of 'Effects effects m'

data Effects a m where

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

data Free effects a

The van Laarhoven-encoded Free Monad with Extensible effects

Instances

Monad (Free effect)

Methods

(>>=) :: Free effect a -> (a -> Free effect b) -> Free effect b

(>>) :: Free effect a -> Free effect b -> Free effect b

return :: a -> Free effect a

fail :: String -> Free effect a

Functor (Free effect)

Methods

fmap :: (a -> b) -> Free effect a -> Free effect b

(<$) :: a -> Free effect b -> Free effect a

Applicative (Free effect)

Methods

pure :: a -> Free effect a

(<*>) :: Free effect (a -> b) -> Free effect a -> Free effect b

(*>) :: Free effect a -> Free effect b -> Free effect b

(<*) :: Free effect a -> Free effect b -> Free effect a

class HasEffect effects effect

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

Minimal complete definition

getEffect

Instances

HasEffect ((:) ((* -> *) -> *) effect effects) effect

An instance of HasEffect that handles the case where our desired effect type matches the head of the list. We then return that effect.

Methods

getEffect :: Effects ((((* -> *) -> *) ': effect) effects) m -> effect m

HasEffect effects effect => HasEffect ((:) ((* -> *) -> *) notIt effects) effect

An instance of HasEffect that handles the case where our desired effect type doesn't match the head of the HList.

Methods

getEffect :: Effects ((((* -> *) -> *) ': notIt) effects) m -> effect m

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

Tear down a Free Monad using the supplied effects value.

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

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