Package fj.control.parallel
Class Promise<A>
- java.lang.Object
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- fj.control.parallel.Promise<A>
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public final class Promise<A> extends java.lang.Object
Represents a non-blocking future value. Products, functions, and actors, given to the methods on this class, are executed concurrently, and the Promise serves as a handle on the result of the computation. Provides monadic operations so that future computations can be combined Author: Runar
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description <B> Promise<B>
apply(Promise<F<A,B>> pf)
Performs function application within a promise (applicative functor pattern).<B,C>
Promise<C>bind(Promise<B> pb, F<A,F<B,C>> f)
Binds the given function to this promise and the given promise, with a final join.<B> Promise<B>
bind(F<A,Promise<B>> f)
Binds the given function over this promise, with a final join.<B,C>
Promise<C>bind(P1<Promise<B>> p, F<A,F<B,C>> f)
Binds the given function to this promise and the given promise, with a final join.A
claim()
Waits if necessary for the computation to complete, and then retrieves its result.Option<A>
claim(long timeout, java.util.concurrent.TimeUnit unit)
Waits if necessary for the computation to complete, and then retrieves its result.<B> Promise<B>
cobind(F<Promise<A>,B> f)
Binds the given function across a promise of this promise (Comonad pattern).Promise<Promise<A>>
cojoin()
Duplicates this promise to a promise of itself (Comonad pattern).<B> Promise<B>
fmap(F<A,B> f)
Provides a promise to apply the given function to this promise's future value (covariant functor pattern).static <A,B>
F<Promise<A>,Promise<B>>fmap_(F<A,B> f)
Promotes any function to a transformation between promises (covariant functor pattern).static <A,B>
F<List<A>,Promise<B>>foldRight(Strategy<Unit> s, F<A,F<B,B>> f, B b)
Performs a right-fold reduction across a list in constant stack space.static <A,B>
F<Stream<A>,Promise<B>>foldRightS(Strategy<Unit> s, F<A,F<P1<B>,B>> f, B b)
Performs a right-fold reduction across a Stream in constant stack space.boolean
isFulfilled()
Returns true if this promise has been fulfilled.static <A> Promise<A>
join(Promise<Promise<A>> p)
Turns a promise of a promise into just a promise.static <A> Promise<A>
join(Strategy<Unit> s, P1<Promise<A>> p)
Turns a product of a promise into just a promise.static <A,B,C>
F<Promise<A>,F<Promise<B>,Promise<C>>>liftM2(F<A,F<B,C>> f)
Promotes a function of arity-2 to a function on promises.private static <A> Promise<A>
mkPromise(Strategy<Unit> s)
static <A> F<P1<A>,Promise<A>>
promise(Strategy<Unit> s)
Provides a first-class unit function for promises.static <A,B>
F<A,Promise<B>>promise(Strategy<Unit> s, F<A,B> f)
Transforms any function so that it returns a promise of a value instead of an actual value.static <A> Promise<A>
promise(Strategy<Unit> s, P1<A> a)
Promises to provide the value of the given 1-product, in the future.static <A> Promise<java.util.concurrent.Callable<A>>
promise(Strategy<Unit> s, java.util.concurrent.Callable<A> a)
Provides a promise to call the given Callable in the future.static <A> F<List<Promise<A>>,Promise<List<A>>>
sequence(Strategy<Unit> s)
First-class version of the sequence function through a List.static <A> Promise<List<A>>
sequence(Strategy<Unit> s, List<Promise<A>> as)
Turns a List of promises into a single promise of a List.static <A> Promise<Stream<A>>
sequence(Strategy<Unit> s, Stream<Promise<A>> as)
Turns a Stream of promises into a single promise of a Stream.static <A> Promise<P1<A>>
sequence(Strategy<Unit> s, P1<Promise<A>> p)
Transforms a product of a promise to a promise of a product.static <A> F<List<Promise<A>>,Promise<List<A>>>
sequenceS(Strategy<Unit> s)
First-class version of the sequence function through a Stream.<B> Stream<B>
sequenceW(Stream<F<Promise<A>,B>> fs)
Applies a stream of comonadic functions to this promise, returning a stream of values.void
to(Actor<A> a)
Promises to send a value to the given actor in the future.
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Method Detail
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promise
public static <A> Promise<A> promise(Strategy<Unit> s, P1<A> a)
Promises to provide the value of the given 1-product, in the future. Represents the unit function for promises.- Parameters:
s
- The strategy with which to fulfil the promise.a
- The 1-product to evaluate concurrently.- Returns:
- A promise representing the future result of evaluating the given 1-product.
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promise
public static <A> F<P1<A>,Promise<A>> promise(Strategy<Unit> s)
Provides a first-class unit function for promises.- Parameters:
s
- The strategy with which to fulfil promises.- Returns:
- A function that, given a 1-product, yields a promise of that product's value.
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promise
public static <A> Promise<java.util.concurrent.Callable<A>> promise(Strategy<Unit> s, java.util.concurrent.Callable<A> a)
Provides a promise to call the given Callable in the future.- Parameters:
s
- The strategy with which to fulfil the promise.a
- The Callable to evaluate concurrently.- Returns:
- A promise of a new Callable that will return the result of calling the given Callable.
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promise
public static <A,B> F<A,Promise<B>> promise(Strategy<Unit> s, F<A,B> f)
Transforms any function so that it returns a promise of a value instead of an actual value. Represents the Kleisli arrow for the Promise monad.- Parameters:
s
- The strategy with which to fulfil the promise.f
- The function to turn into a promise-valued function.- Returns:
- The given function transformed into a function that returns a promise.
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to
public void to(Actor<A> a)
Promises to send a value to the given actor in the future.- Parameters:
a
- An actor that will receive this Promise's value in the future.
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fmap
public <B> Promise<B> fmap(F<A,B> f)
Provides a promise to apply the given function to this promise's future value (covariant functor pattern).- Parameters:
f
- The function to apply to this promise's future value.- Returns:
- A promise representing the future result of applying the given function to this promised value.
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fmap_
public static <A,B> F<Promise<A>,Promise<B>> fmap_(F<A,B> f)
Promotes any function to a transformation between promises (covariant functor pattern).- Parameters:
f
- The function to promote to a transformation between promises.- Returns:
- That function lifted to a function on Promises.
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join
public static <A> Promise<A> join(Promise<Promise<A>> p)
Turns a promise of a promise into just a promise. The join function for the Promise monad. Promise to give it a Promise of an A, and it will promise you an A in return.- Parameters:
p
- A promise of a promise.- Returns:
- The promised promise.
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join
public static <A> Promise<A> join(Strategy<Unit> s, P1<Promise<A>> p)
Turns a product of a promise into just a promise. Does not block on the product by calling it, but creates a new promise with a final join.- Parameters:
s
- The strategy with which to fulfil the promise.p
- A product-1 of a promise to turn into just a promise.- Returns:
- The joined promise.
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bind
public <B> Promise<B> bind(F<A,Promise<B>> f)
Binds the given function over this promise, with a final join. The bind function for the Promise monad.- Parameters:
f
- The function to bind over this promise.- Returns:
- The result of applying the given function to this promised value.
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apply
public <B> Promise<B> apply(Promise<F<A,B>> pf)
Performs function application within a promise (applicative functor pattern).- Parameters:
pf
- The promised function to apply.- Returns:
- A new promise after applying the given promised function to this promise.
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bind
public <B,C> Promise<C> bind(Promise<B> pb, F<A,F<B,C>> f)
Binds the given function to this promise and the given promise, with a final join.- Parameters:
pb
- A promise with which to bind the given function.f
- The function to apply to the given promised values.- Returns:
- A new promise after performing the map, then final join.
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bind
public <B,C> Promise<C> bind(P1<Promise<B>> p, F<A,F<B,C>> f)
Binds the given function to this promise and the given promise, with a final join.- Parameters:
p
- A promise with which to bind the given function.f
- The function to apply to the given promised values.- Returns:
- A new promise after performing the map, then final join.
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liftM2
public static <A,B,C> F<Promise<A>,F<Promise<B>,Promise<C>>> liftM2(F<A,F<B,C>> f)
Promotes a function of arity-2 to a function on promises.- Parameters:
f
- The function to promote.- Returns:
- A function of arity-2 promoted to map over promises.
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sequence
public static <A> Promise<List<A>> sequence(Strategy<Unit> s, List<Promise<A>> as)
Turns a List of promises into a single promise of a List.- Parameters:
s
- The strategy with which to sequence the promises.as
- The list of promises to transform.- Returns:
- A single promise for the given List.
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sequence
public static <A> F<List<Promise<A>>,Promise<List<A>>> sequence(Strategy<Unit> s)
First-class version of the sequence function through a List.- Parameters:
s
- The strategy with which to sequence a given list of promises.- Returns:
- A function that turns a list of promises into a single promise of a list.
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sequence
public static <A> Promise<Stream<A>> sequence(Strategy<Unit> s, Stream<Promise<A>> as)
Turns a Stream of promises into a single promise of a Stream.- Parameters:
s
- The strategy with which to sequence the promises.as
- The Stream of promises to transform.- Returns:
- A single promise for the given Stream.
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sequenceS
public static <A> F<List<Promise<A>>,Promise<List<A>>> sequenceS(Strategy<Unit> s)
First-class version of the sequence function through a Stream.- Parameters:
s
- The strategy with which to sequence a given Stream of promises.- Returns:
- A function that turns a list of promises into a single promise of a Stream..
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sequence
public static <A> Promise<P1<A>> sequence(Strategy<Unit> s, P1<Promise<A>> p)
Transforms a product of a promise to a promise of a product.- Parameters:
s
- The strategy with which to traverse the promise.p
- A product of a promise to traverse.- Returns:
- A promised product.
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foldRight
public static <A,B> F<List<A>,Promise<B>> foldRight(Strategy<Unit> s, F<A,F<B,B>> f, B b)
Performs a right-fold reduction across a list in constant stack space.- Parameters:
s
- The strategy with which to fold the list.f
- The function to apply on each element of the list.b
- The beginning value to start the application from.- Returns:
- The final result after the right-fold reduction.
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foldRightS
public static <A,B> F<Stream<A>,Promise<B>> foldRightS(Strategy<Unit> s, F<A,F<P1<B>,B>> f, B b)
Performs a right-fold reduction across a Stream in constant stack space.- Parameters:
s
- The strategy with which to fold the Stream.f
- The function to apply on each element of the Stream.b
- The beginning value to start the application from.- Returns:
- The final result after the right-fold reduction.
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claim
public A claim()
Waits if necessary for the computation to complete, and then retrieves its result.- Returns:
- The promised value.
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claim
public Option<A> claim(long timeout, java.util.concurrent.TimeUnit unit)
Waits if necessary for the computation to complete, and then retrieves its result.- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Returns:
- The promised value, or none if the timeout was reached.
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isFulfilled
public boolean isFulfilled()
Returns true if this promise has been fulfilled.- Returns:
- true if this promise has been fulfilled.
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cobind
public <B> Promise<B> cobind(F<Promise<A>,B> f)
Binds the given function across a promise of this promise (Comonad pattern).- Parameters:
f
- A function to apply within a new promise of this promise.- Returns:
- A new promise of the result of applying the given function to this promise.
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cojoin
public Promise<Promise<A>> cojoin()
Duplicates this promise to a promise of itself (Comonad pattern).- Returns:
- a promise of this promise.
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sequenceW
public <B> Stream<B> sequenceW(Stream<F<Promise<A>,B>> fs)
Applies a stream of comonadic functions to this promise, returning a stream of values.- Parameters:
fs
- A stream of functions to apply to this promise.- Returns:
- A stream of the results of applying the given stream of functions to this promise.
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