FRP.Sodium.Context

Generalization of the Sodium API to allow for parallel processing.

Documentation

class (Applicative (Reactive r), Monad (Reactive r), MonadFix (Reactive r), Functor (Event r), Applicative (Behavior r)) => Context r where

Associated Types

data Reactive r :: * -> *

A monad for transactional reactive operations. Execute it from IO using sync.

data Event r :: * -> *

A stream of events. The individual firings of events are called 'event occurrences'.

data Behavior r :: * -> *

A time-varying value, American spelling.

Methods

sync :: Reactive r a -> IO a

Execute the specified Reactive within a new transaction, blocking the caller until all resulting processing is complete and all callbacks have been called. This operation is thread-safe, so it may be called from any thread.

State changes to hold values occur after processing of the transaction is complete.

newEvent :: Reactive r (Event r a, a -> Reactive r ())

Returns an event, and a push action for pushing a value into the event.

listen :: Event r a -> (a -> IO ()) -> Reactive r (IO ())

Listen for firings of this event. The returned IO () is an IO action that unregisters the listener. This is the observer pattern.

To listen to a Behavior use listen (value b) handler

never :: Event r a

An event that never fires.

merge :: Event r a -> Event r a -> Event r a

Merge two streams of events of the same type.

In the case where two event occurrences are simultaneous (i.e. both within the same transaction), both will be delivered in the same transaction. If the event firings are ordered for some reason, then their ordering is retained. In many common cases the ordering will be undefined.

filterJust :: Event r (Maybe a) -> Event r a

Unwrap Just values, and discard event occurrences with Nothing values.

hold :: a -> Event r a -> Reactive r (Behavior r a)

Create a behavior with the specified initial value, that gets updated by the values coming through the event. The 'current value' of the behavior is notionally the value as it was 'at the start of the transaction'. That is, state updates caused by event firings get processed at the end of the transaction.

updates :: Behavior r a -> Event r a

An event that gives the updates for the behavior. If the behavior was created with hold, then updates gives you an event equivalent to the one that was held.

value :: Behavior r a -> Event r a

An event that is guaranteed to fire once when you listen to it, giving the current value of the behavior, and thereafter behaves like changes, firing for each update to the behavior's value.

snapshot :: (a -> b -> c) -> Event r a -> Behavior r b -> Event r c

Sample the behavior at the time of the event firing. Note that the 'current value' of the behavior that's sampled is the value as at the start of the transaction before any state changes of the current transaction are applied through holds.

switchE :: Behavior r (Event r a) -> Event r a

Unwrap an event inside a behavior to give a time-varying event implementation.

switch :: Behavior r (Behavior r a) -> Reactive r (Behavior r a)

Unwrap a behavior inside another behavior to give a time-varying behavior implementation.

execute :: Event r (Reactive r a) -> Event r a

Execute the specified Reactive action inside an event.

sample :: Behavior r a -> Reactive r a

Obtain the current value of a behavior.

coalesce :: (a -> a -> a) -> Event r a -> Event r a

If there's more than one firing in a single transaction, combine them into one using the specified combining function.

If the event firings are ordered, then the first will appear at the left input of the combining function. In most common cases it's best not to make any assumptions about the ordering, and the combining function would ideally be commutative.

once :: Event r a -> Event r a

Throw away all event occurrences except for the first one.

split :: Event r [a] -> Event r a

Take each list item and put it into a new transaction of its own.

An example use case of this might be a situation where we are splitting a block of input data into frames. We obviously want each frame to have its own transaction so that state is updated separately each frame.

Instances

Context Plain

class Context r => ContextIO r where

Methods

executeAsyncIO :: Event r (IO a) -> Event r a

Execute the specified IO operation asynchronously on a separate thread, and signal the output event in a new transaction upon its completion.

Caveat: Where switch or switchE is used, when some reactive logic has been switched away, we rely on garbage collection to actually disconnect this logic from any input it may be listening to. With normal Sodium code, everything is pure, so before garbage collection happens, the worst we will get is some wasted CPU cycles. If you are using 'executeAsyncIO'/'executeSyncIO' inside a switch or switchE, however, it is possible that logic that has been switched away hasn't been garbage collected yet. This logic could still run, and if it has observable effects, you could see it running after it is supposed to have been switched out. One way to avoid this is to pipe the source event for IO out of the switch, run the 'executeAsyncIO'/'executeSyncIO' outside the switch, and pipe its output back into the switch contents.

executeSyncIO :: Event r (IO a) -> Event r a

Execute the specified IO operation synchronously and fire the output event in the same transaction.

Caveat: See executeAsyncIO.

type Behaviour r a = Behavior r a

A time-varying value, British spelling.

newBehavior

Arguments

:: forall r a . Context r

=> a

Initial behavior value

-> Reactive r (Behavior r a, a -> Reactive r ())

Create a new Behavior along with an action to push changes into it. American spelling.

newBehaviour

Arguments

:: forall r a . Context r

=> a

Initial behavior value

-> Reactive r (Behavior r a, a -> Reactive r ())

Create a new Behavior along with an action to push changes into it. British spelling.

mergeWith :: Context r => (a -> a -> a) -> Event r a -> Event r a -> Event r a

Merge two streams of events of the same type, combining simultaneous event occurrences.

In the case where multiple event occurrences are simultaneous (i.e. all within the same transaction), they are combined using the same logic as coalesce.

filterE :: Context r => (a -> Bool) -> Event r a -> Event r a

Only keep event occurrences for which the predicate returns true.

gate :: Context r => Event r a -> Behavior r Bool -> Event r a

Let event occurrences through only when the behavior's value is True. Note that the behavior's value is as it was at the start of the transaction, that is, no state changes from the current transaction are taken into account.

collectE :: Context r => (a -> s -> (b, s)) -> s -> Event r a -> Reactive r (Event r b)

Transform an event with a generalized state loop (a mealy machine). The function is passed the input and the old state and returns the new state and output value.

collect :: Context r => (a -> s -> (b, s)) -> s -> Behavior r a -> Reactive r (Behavior r b)

Transform a behavior with a generalized state loop (a mealy machine). The function is passed the input and the old state and returns the new state and output value.

accum :: Context r => a -> Event r (a -> a) -> Reactive r (Behavior r a)

Accumulate state changes given in the input event.