reactive-0.9.4: Simple foundation for functional reactive programmingSource codeContentsIndex
FRP.Reactive.Future
Stabilityexperimental
Maintainerconal@conal.net
Contents
Time & futures
Tests
Description

A simple formulation of functional futures, roughly as described at http://en.wikipedia.org/wiki/Futures_and_promises.

A future is a value with an associated time of arrival. Typically, neither the time nor the value can be known until the arrival time.

Primitive futures can be things like /the value of the next key you press, or the value of LambdaPix stock at noon next Monday/.

Composition is via standard type classes: Functor, Applicative, Monad, and Monoid. Some comments on the Future instances of these classes:

  • Monoid: mempty is a future that never arrives (infinite time and undefined value), and a mappend b is the earlier of a and b, preferring a when simultaneous.
  • Functor: apply a function to a future argument. The (future) result arrives simultaneously with the argument.
  • Applicative: pure gives value arriving negative infinity. '(<*>)' applies a future function to a future argument, yielding a future result that arrives once both function and argument have arrived (coinciding with the later of the two times).
  • Monad: return is the same as pure (as usual). (>>=) cascades futures. join resolves a future future value into a future value.

Futures are parametric over time as well as value types. The time parameter can be any ordered type and is particularly useful with time types that have rich partial information structure, such as /improving values/.

Synopsis
type Time t = Max (AddBounds t)
ftime :: t -> Time t
newtype FutureG t a = Future {
unFuture :: (Time t, a)
}
inFuture :: ((Time t, a) -> (Time t', b)) -> FutureG t a -> FutureG t' b
inFuture2 :: ((Time t, a) -> (Time t', b) -> (Time t', c)) -> FutureG t a -> FutureG t' b -> FutureG t' c
futTime :: FutureG t a -> Time t
futVal :: FutureG t a -> a
future :: t -> a -> FutureG t a
withTimeF :: FutureG t a -> FutureG t (Time t, a)
batch :: TestBatch
Time & futures
type Time t = Max (AddBounds t)Source
Time used in futures. The parameter t can be any Ord type. The added bounds represent -Infinity and +Infinity. Pure values have time minBound (-Infinity), while never-occurring futures have time maxBound (+Infinity).
ftime :: t -> Time tSource
Make a finite time
newtype FutureG t a Source
A future value of type a with time type t. Simply a time/value pair. Particularly useful with time types that have non-flat structure.
Constructors
Future
unFuture :: (Time t, a)
show/hide Instances
inFuture :: ((Time t, a) -> (Time t', b)) -> FutureG t a -> FutureG t' bSource
Apply a unary function within the FutureG representation.
inFuture2 :: ((Time t, a) -> (Time t', b) -> (Time t', c)) -> FutureG t a -> FutureG t' b -> FutureG t' cSource
Apply a binary function within the FutureG representation.
futTime :: FutureG t a -> Time tSource
A future's time
futVal :: FutureG t a -> aSource
A future's value
future :: t -> a -> FutureG t aSource
A future value with given time & value
withTimeF :: FutureG t a -> FutureG t (Time t, a)Source
Access time of future
Tests
batch :: TestBatchSource
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