Control.Monad.Freer.Internal

Internal machinery for this effects library. This includes:

• Eff data type, for expressing effects
• NonDetEff data type, for nondeterministic effects
• Functions for facilitating the construction of effects and their handlers

Using http://okmij.org/ftp/Haskell/extensible/Eff1.hs as a starting point.

Documentation

data Eff r a

The Eff representation.

Status of a coroutine (client): * Val: Done with the value of type a * E : Sending a request of type Union r with the continuation Arrs r b a

Constructors

Val a

forall b . E (Union r b) (Arrs r b a)

Instances

Monad (Eff r)

Functor (Eff r)

Applicative (Eff r)

Member NonDetEff r => Alternative (Eff r)

Member NonDetEff r => MonadPlus (Eff r)

class Member' t r (FindElem t r) => Member t r where

Methods

inj :: t v -> Union r v

prj :: Union r v -> Maybe (t v)

Instances

Member' t r (FindElem t r) => Member t r

type family Members m r :: Constraint

Equations

Members (t : c) r = (Member t r, Members c r)

Members `[]` r = ()

type Arr r a b = a -> Eff r b

Effectful arrow type: a function from a to b that also does effects denoted by r

type Arrs r a b = FTCQueue (Eff r) a b

An effectful function from a to b that is a composition of several effectful functions. The paremeter r describes the overall effect. The composition members are accumulated in a type-aligned queue.

data Union r v

data NonDetEff a where

A data type for representing nondeterminstic choice

Constructors

MZero :: NonDetEff a

MPlus :: NonDetEff Bool

makeChoiceA :: Alternative f => Eff (NonDetEff : r) a -> Eff r (f a)

A handler for nondeterminstic effects

msplit :: Member NonDetEff r => Eff r a -> Eff r (Maybe (a, Eff r a))

decomp :: Union (t : r) v -> Either (Union r v) (t v)

tsingleton :: (a -> m b) -> FTCQueue m a b

Build a leaf from a single operation [O(1)]

qApp :: Arrs r b w -> b -> Eff r w

Function application in the context of an array of effects, Arrs r b w

qComp :: Arrs r a b -> (Eff r b -> Eff r' c) -> Arr r' a c

Composition of effectful arrows Allows for the caller to change the effect environment, as well

send :: Member t r => t v -> Eff r v

send a request and wait for a reply

run :: Eff `[]` w -> w

Runs a set of Effects. Requires that all effects are consumed. Typically composed as follows: > run . runEff1 eff1Arg . runEff2 eff2Arg1 eff2Arg2 (program)

handleRelay :: (a -> Eff r w) -> (forall v. t v -> Arr r v w -> Eff r w) -> Eff (t : r) a -> Eff r w

Given a request, either handle it or relay it.

handleRelayS :: s -> (s -> a -> Eff r w) -> (forall v. s -> t v -> (s -> Arr r v w) -> Eff r w) -> Eff (t : r) a -> Eff r w

Parameterized handleRelay Allows sending along some state to be handled for the target effect, or relayed to a handler that can handle the target effect.

interpose :: Member t r => (a -> Eff r w) -> (forall v. t v -> Arr r v w -> Eff r w) -> Eff r a -> Eff r w

Intercept the request and possibly reply to it, but leave it unhandled