Control.Eff.Concurrent.Api.Observer

Observer Effects

This module supports the implementation of observers and observables. Expected use case is event propagation.

Since: 0.16.0

Documentation

data Observer o where

Describes a process that observes another via Asynchronous Api messages.

An observer consists of a filter and a process id. The filter converts an observation to a message understood by the observer process, and the ProcessId is used to send the message.

Since: 0.16.0

Constructors

Observer :: (Show (Server p), Typeable p, Typeable o) => (o -> Maybe (Api p Asynchronous)) -> Server p -> Observer o

Instances

Eq (Observer o)

Defined in Control.Eff.Concurrent.Api.Observer

Methods

(==) :: Observer o -> Observer o -> Bool

(/=) :: Observer o -> Observer o -> Bool

Ord (Observer o)

Defined in Control.Eff.Concurrent.Api.Observer

Methods

compare :: Observer o -> Observer o -> Ordering

(<) :: Observer o -> Observer o -> Bool

(<=) :: Observer o -> Observer o -> Bool

(>) :: Observer o -> Observer o -> Bool

(>=) :: Observer o -> Observer o -> Bool

max :: Observer o -> Observer o -> Observer o

min :: Observer o -> Observer o -> Observer o

Show (Observer o)

Defined in Control.Eff.Concurrent.Api.Observer

Methods

showsPrec :: Int -> Observer o -> ShowS

show :: Observer o -> String

showList :: [Observer o] -> ShowS

data Api (Observer o) r

A minimal Api for handling observations. This is one simple way of receiving observations - of course users can use any other Asynchronous Api message type for receiving observations.

Since: 0.16.0

Defined in Control.Eff.Concurrent.Api.Observer

data Api (Observer o) r where

• Observed :: forall o (r :: Synchronicity). o -> Api (Observer o) Asynchronous

data family Api (api :: Type) (reply :: Synchronicity)

This data family defines an API, a communication interface description between at least two processes. The processes act as servers or client(s) regarding a specific instance of this type.

The first parameter is usually a user defined phantom type that identifies the Api instance.

The second parameter specifies if a specific constructor of an (GADT-like) Api instance is Synchronous, i.e. returns a result and blocks the caller or if it is Asynchronous

Example:

data BookShop deriving Typeable

data instance Api BookShop r where
  RentBook  :: BookId   -> Api BookShop ('Synchronous (Either RentalError RentalId))
  BringBack :: RentalId -> Api BookShop 'Asynchronous

type BookId = Int
type RentalId = Int
type RentalError = String

Instances

data Api (Observer o) r

A minimal Api for handling observations. This is one simple way of receiving observations - of course users can use any other Asynchronous Api message type for receiving observations.

Since: 0.16.0

Defined in Control.Eff.Concurrent.Api.Observer

data Api (Observer o) r where

• Observed :: forall o (r :: Synchronicity). o -> Api (Observer o) Asynchronous

data Api (ObserverRegistry o) r

Api for managing observers. This can be added to any server for any number of different observation types. The functions manageObservers and handleObserverRegistration are used to include observer handling;

Since: 0.16.0

Defined in Control.Eff.Concurrent.Api.Observer

data Api (ObserverRegistry o) r where

• RegisterObserver :: forall k (o :: k) (r :: Synchronicity) o. Observer o -> Api (ObserverRegistry o) Asynchronous
• ForgetObserver :: forall k (o :: k) (r :: Synchronicity) o. Observer o -> Api (ObserverRegistry o) Asynchronous

registerObserver :: (SetMember Process (Process q) r, HasCallStack, Member Interrupts r, Typeable o) => Observer o -> Server (ObserverRegistry o) -> Eff r ()

And an Observer to the set of recipients for all observations reported by observed. Note that the observers are keyed by the observing process, i.e. a previous entry for the process contained in the Observer is overwritten. If you want multiple entries for a single process, just combine several filter functions.

Since: 0.16.0

forgetObserver :: (SetMember Process (Process q) r, HasCallStack, Member Interrupts r, Typeable o) => Observer o -> Server (ObserverRegistry o) -> Eff r ()

Send the ForgetObserver message

Since: 0.16.0

handleObservations :: (HasCallStack, Typeable o, SetMember Process (Process q) r) => (o -> Eff r CallbackResult) -> MessageCallback (Observer o) r

Based on the Api instance for Observer this simplified writing a callback handler for observations. In order to register to and ObserverRegistry use toObserver.

Since: 0.16.0

toObserver :: Typeable o => Server (Observer o) -> Observer o

Use a Server as an Observer for handleObservations.

Since: 0.16.0

toObserverFor :: (Typeable a, Typeable o) => (o -> Api a Asynchronous) -> Server a -> Observer o

Create an Observer that conditionally accepts all observations of the given type and applies the given function to them; the function takes an observation and returns an Api cast that the observer server is compatible to.

Since: 0.16.0

data ObserverRegistry o

An Api for managing Observers, encompassing registration and de-registration of Observers.

Since: 0.16.0

Instances

data Api (ObserverRegistry o) r

Api for managing observers. This can be added to any server for any number of different observation types. The functions manageObservers and handleObserverRegistration are used to include observer handling;

Since: 0.16.0

Defined in Control.Eff.Concurrent.Api.Observer

data Api (ObserverRegistry o) r where

• RegisterObserver :: forall k (o :: k) (r :: Synchronicity) o. Observer o -> Api (ObserverRegistry o) Asynchronous
• ForgetObserver :: forall k (o :: k) (r :: Synchronicity) o. Observer o -> Api (ObserverRegistry o) Asynchronous

type ObserverState o = State (Observers o)

Alias for the effect that contains the observers managed by manageObservers

handleObserverRegistration :: forall o q r. (HasCallStack, Typeable o, SetMember Process (Process q) r, Member (ObserverState o) r) => MessageCallback (ObserverRegistry o) r

Provide the implementation for the ObserverRegistry Api, this handled RegisterObserver and ForgetObserver messages. It also adds the ObserverState constraint to the effect list.

Since: 0.16.0

manageObservers :: Eff (ObserverState o ': r) a -> Eff r a

Keep track of registered Observers.

Handle the ObserverState introduced by handleObserverRegistration.

Since: 0.16.0

observed :: forall o r q. (SetMember Process (Process q) r, Member (ObserverState o) r, Member Interrupts r) => o -> Eff r ()

Report an observation to all observers. The process needs to manageObservers and to handleObserverRegistration.

Since: 0.16.0