FRP.Event

fix :: forall o i. (Event i -> { input :: Event i, output :: Event o }) -> Event o

Compute a fixed point

fold :: forall b a. (a -> b -> b) -> Event a -> b -> Event b

Fold over values received from some Event, creating a new Event.

keepLatest :: forall a. Event (Event a) -> Event a

Flatten a nested Event, reporting values only from the most recent inner Event.

sampleOn :: forall b a. Event a -> Event (a -> b) -> Event b

Create an Event which samples the latest values from the first event at the times when the second event fires.

newtype Event a

An Event represents a collection of discrete occurrences with associated times. Conceptually, an Event is a (possibly-infinite) list of values-and-times:

type Event a = List { value :: a, time :: Time }

Events are created from real events like timers or mouse clicks, and then combined using the various functions and instances provided in this module.

Events are consumed by providing a callback using the subscribe function.

Instances

• Functor Event
• Compactable Event
• Filterable Event
• Apply Event
• Applicative Event
• Alt Event
• Plus Event
• Alternative Event
• (Semigroup a) => Semigroup (Event a)
• (Monoid a) => Monoid (Event a)
• IsEvent Event

create :: forall a. Effect { event :: Event a, push :: a -> Effect Unit }

Create an event and a function which supplies a value to that event.

makeEvent :: forall a. ((a -> Effect Unit) -> Effect (Effect Unit)) -> Event a

Make an Event from a function which accepts a callback and returns an unsubscription function.

Note: you probably want to use create instead, unless you need explicit control over unsubscription.

subscribe :: forall a r. Event a -> (a -> Effect r) -> Effect (Effect Unit)

Subscribe to an Event by providing a callback.

subscribe returns a canceller function.

class (Compactable f, Functor f) <= Filterable f  where

Filterable represents data structures which can be partitioned/filtered.

• partitionMap - partition a data structure based on an either predicate.
• partition - partition a data structure based on boolean predicate.
• filterMap - map over a data structure and filter based on a maybe.
• filter - filter a data structure based on a boolean.

Laws:

• Functor Relation: filterMap identity ≡ compact

• Functor Identity: filterMap Just ≡ identity

• Kleisli Composition: filterMap (l <=< r) ≡ filterMap l <<< filterMap r

• filter ≡ filterMap <<< maybeBool

• filterMap p ≡ filter (isJust <<< p)

• Functor Relation: partitionMap identity ≡ separate

• Functor Identity 1: _.right <<< partitionMap Right ≡ identity

• Functor Identity 2: _.left <<< partitionMap Left ≡ identity

• f <<< partition ≡ partitionMap <<< eitherBool where f = \{ no, yes } -> { left: no, right: yes }

• f <<< partitionMap p ≡ partition (isRight <<< p) where f = \{ left, right } -> { no: left, yes: right}

Default implementations are provided by the following functions:

• partitionDefault
• partitionDefaultFilter
• partitionDefaultFilterMap
• partitionMapDefault
• filterDefault
• filterDefaultPartition
• filterDefaultPartitionMap
• filterMapDefault

Members

• filterMap :: forall b a. (a -> Maybe b) -> f a -> f b

Instances

• Filterable Array
• Filterable Maybe
• (Monoid m) => Filterable (Either m)
• Filterable List
• (Ord k) => Filterable (Map k)

class (Alternative event, Filterable event) <= IsEvent event  where

Functions which an Event type should implement:

• fold: combines incoming values using the specified function, starting with the specific initial value.
• keepLatest flattens a nested event, reporting values only from the most recent inner event.
• sampleOn: samples an event at the times when a second event fires.
• fix: compute a fixed point, by feeding output events back in as inputs.

Members

• fold :: forall b a. (a -> b -> b) -> event a -> b -> event b
• keepLatest :: forall a. event (event a) -> event a
• sampleOn :: forall b a. event a -> event (a -> b) -> event b
• fix :: forall o i. (event i -> { input :: event i, output :: event o }) -> event o

withLast :: forall a event. IsEvent event => event a -> event { last :: Maybe a, now :: a }

Compute differences between successive event values.

sampleOn_ :: forall b a event. IsEvent event => event a -> event b -> event a

Create an Event which samples the latest values from the first event at the times when the second event fires, ignoring the values produced by the second event.

mapAccum :: forall c b a event. IsEvent event => (a -> b -> Tuple b c) -> event a -> b -> event c

Map over an event with an accumulator.

For example, to keep the index of the current event:

mapAccum (\x i -> Tuple (i + 1) (Tuple x i)) 0`.

gateBy :: forall event b a. IsEvent event => (Maybe a -> b -> Boolean) -> event a -> event b -> event b

Generalised form of gateBy, allowing for any predicate between the two events. Until a value from the first event is received, Nothing will be passed to the predicate.

gate :: forall event a. IsEvent event => event Boolean -> event a -> event a

Sample the events that are fired while a boolean event is true. Note that, until the boolean event fires, it will be assumed to be false, and events will be blocked.

folded :: forall a event. IsEvent event => Monoid a => event a -> event a

Combine subsequent events using a Monoid.

count :: forall a event. IsEvent event => event a -> event Int

Count the number of events received.