Fluture offers a control structure similar to Promises, Tasks, Deferreds, and what-have-you. Let's call them Futures.
Much like Promises, Futures represent the value arising from the success or failure of an asynchronous operation (I/O). Though unlike Promises, Futures are lazy and adhere to the monadic interface.
Some of the features provided by Fluture include:
For more information:
npm install --save fluture
Fluture depends on these functions being present:
Object.create,
Object.assign and Array.isArray.
You may need to polyfill one or more.
var fs = require('fs');
var Future = require('fluture');
var getPackageName = function(file){
return Future.node(function(done){ fs.readFile(file, 'utf8', done) })
.chain(Future.encase(JSON.parse))
.map(function(x){ return x.name });
};
getPackageName('package.json')
.fork(console.error, console.log);
//> "fluture"
The package.json sets a module-field for build-tools like Rollup. The
module version also has TypeScript definitions.
import {readFile} from 'fs';
import {node, encase} from 'fluture';
const getPackageName = file =>
node(done => { readFile(file, 'utf8', done) })
.chain(encase(JSON.parse))
.map(x => x.name);
getPackageName('package.json')
.fork(console.error, console.log);
//> "fluture"
Fluture is hosted in full with all of its dependencies at https://rawgit.com/fluture-js/Fluture/master/dist/bundle.js.
This script will add Fluture to the global scope.
Future implements Fantasy Land and Static Land -compatible
Bifunctor, Monad and ChainRec (of, ap, map, bimap, chain, chainRec).
All versions of Fantasy Land are supported.Future.Par implements Fantasy Land 3 and Static Land -compatible
Alternative (of, zero, map, ap, alt).@@type properties
for Sanctuary Type Identifiers.The name "Fluture" is a conjunction of "FL" (the acronym to Fantasy Land) and "future". Fluture means butterfly in Romanian: A creature you might expect to see in Fantasy Land.
Thanks to Erik Fuente for the logo, and WEAREREASONABLEPEOPLE for sponsoring the project.
Future: Create a possibly cancellable Futureof: Create a resolved Futurereject: Create a rejected Futureafter: Create a Future that resolves after a timeoutrejectAfter: Create a Future that rejects after a timeoutdo: Create a "coroutine" using a generator functiontry: Create a Future using a possibly throwing functiontryP: Create a Future using a Promise-returning functionnode: Create a Future using a Node-style callbackencase: Convert a possibly throwing function to a Future functionencaseP: Convert a Promise-retuning function to a Future functionencaseN: Convert a Nodeback function to a Future functionmap: Synchronously process the success value in a Futurebimap: Synchronously process the success or failure value in a Futurechain: Asynchronously process the success value in a Futureswap: Swap the success with the failure valuemapRej: Synchronously process the failure value in a FuturechainRej: Asynchronously process the failure value in a Futurefold: Coerce success and failure values into the same success valueap: Combine the success values of multiple Futures using a functionand: Logical and for Futuresor: Logical or for FuturesHindley-Milner type signatures are used to document functions. You might encounter some additional syntax that we use to describe JavaScript specific stuff, like methods or functions that take multiple arguments at once.
In order to document methods, we use the squiggly arrow (~>). This separates
the implicit this argument from the other, explicit, arguments. For example,
the following line signifies a function, because it doesn't have a squiggly
arrow in its signature:
map :: (b -> c) -> Future a b -> Future a c
Whereas the next example is a method. It needs a this as indicated by the
use of the squiggly arrow.
Future.prototype.map :: Future a b ~> (b -> c) -> Future a c
Most functions exposed by Fluture are curried. This is reflected in their type signatures by using an arrow at each step where partial application is possible. For example, the following line signifies a curried function, because it has an arrow after each function argument:
add :: Number -> Number -> Number
We could have chosen to write the above line with "groups of one argument", but we usually leave the grouping brackets out for brevity:
add :: (Number) -> (Number) -> Number
In order to document functions and methods that are not curried, we use grouping to show which arguments have to be provided at the same time:
add :: (Number, Number) -> Number
You'll find that some signatures refer to concrete types, such as Future.
This is reference of the types used throughout the documentation:
Future.Par).(a | Nil, b) -> x.[a, b].next-methods which conform to the Iterator protocol.f which may throw an exception e.Some signatures contain "constrained type variables". These constraints are expressed by means of type classes, specifically those defined by Fantasy Land and verified by Sanctuary Type Classes:
Fluture interprets your transformations in a stack safe way. This means that
none of the following operations raise RangeError: Maximum call stack size exceeded:
const add1 = x => x + 1;
let m = Future.of(1);
for(let i = 0; i < 100000; i++){
m = m.map(add1);
}
m.fork(console.error, console.log);
//> 100001
const m = (function recur(x){
const mx = Future.of(x + 1);
return x < 100000 ? mx.chain(recur) : mx;
}(1));
m.fork(console.error, console.log);
//> 100001
To learn more about memory and stack usage under different types of recursion,
see (or execute) scripts/test-mem.
When using this module with Sanctuary Def (and Sanctuary by extension) you might run into the following issue:
const S = require('sanctuary');
const Future = require('fluture');
S.I(Future.of(1));
//! Since there is no type of which all the above values are members,
//! the type-variable constraint has been violated.
This happens because Sanctuary Def needs to know about the types created by Fluture to determine whether the type-variables are consistent.
To let Sanctuary know about these types, we can obtain the type definitions from
fluture-sanctuary-types and pass them to S.create:
const {create, env} = require('sanctuary');
const {env: flutureEnv} = require('fluture-sanctuary-types');
const Future = require('fluture');
const S = create({checkTypes: true, env: env.concat(flutureEnv)});
S.I(Future.of(1));
//> Future.of(1)
Sometimes you may need to convert one Future to another, for example when the Future was created by another package, or an incompatible version of Fluture.
When isFuture returns false, a conversion is necessary. Usually
the most concise way of doing this is as follows:
const NoFuture = require('incompatible-future');
const incompatible = NoFuture.of('Hello');
//Cast the incompatible Future to our version of Future:
const compatible = Future(incompatible.fork.bind(incompatible));
compatible.both(Future.of('world')).value(console.log);
//> ["Hello", "world"]
Future :: ((a -> x, b -> x) -> Cancel) -> Future a bFuture :: ((a -> x, b -> x) -> Cancel) -> Future a b
Creates a Future with the given computation. A computation is a function which
takes two callbacks. Both are continuations for the computation. The first is
reject, commonly abbreviated to rej. The second resolve, which abbreviates
to res. When the computation is finished (possibly asynchronously) it may call
the appropriate continuation with a failure or success value.
Future(function computation(reject, resolve){
//Asynchronous work:
const x = setTimeout(resolve, 3000, 'world');
//Cancellation:
return () => clearTimeout(x);
});
Additionally, the computation may return a nullary function containing cancellation logic. This function is executed when the Future is cancelled after it's forked.
of :: b -> Future a bof :: b -> Future a b
Future.of :: b -> Future a b
Creates a Future which immediately resolves with the given value. This function is compliant with the Fantasy Land Applicative specification.
const eventualThing = Future.of('world');
eventualThing.fork(
console.error,
thing => console.log(`Hello ${thing}!`)
);
//> "Hello world!"
reject :: a -> Future a breject :: a -> Future a b
Future.reject :: a -> Future a b
Creates a Future which immediately rejects with the given value. Just like of
but for the rejection branch.
after :: Number -> b -> Future a bafter :: Number -> b -> Future a b
Creates a Future which resolves with the given value after n milliseconds.
const eventualThing = Future.after(500, 'world');
eventualThing.fork(console.error, thing => console.log(`Hello ${thing}!`));
//> "Hello world!"
rejectAfter :: Number -> a -> Future a brejectAfter :: Number -> a -> Future a b
Creates a Future which rejects with the given reason after n milliseconds.
const eventualError = Future.rejectAfter(500, new Error('Kaputt!'));
eventualError.fork(err => console.log('Oh no - ' + err.message), console.log);
//! Oh no - Kaputt!
do :: (() -> Iterator) -> Future a bdo :: (() -> Iterator) -> Future a b
go :: (() -> Iterator) -> Future a b
A specialized version of fantasy-do which works only for Futures, but has
the advantage of type-checking and not having to pass Future.of. Another
advantage is that the returned Future can be forked multiple times, as opposed
to with a general fantasy-do solution, where forking the Future a second time
behaves erroneously.
Takes a function which returns an Iterator, commonly a generator-function, and chains every produced Future over the previous.
This allows for writing sequential asynchronous code without the pyramid of doom. It's known as "coroutines" in Promise land, and "do-notation" in Haskell land.
Future.do(function*(){
const thing = yield Future.after(300, 'world');
const message = yield Future.after(300, 'Hello ' + thing);
return message + '!';
})
.fork(console.error, console.log);
//After 600ms:
//> "Hello world!"
Error handling is slightly different in do-notation, you need to fold
the error into your control domain, I recommend folding into an Either:
const attempt = Future.fold(S.Left, S.Right);
const ajaxGet = url => Future.reject('Failed to load ' + url);
Future.do(function*(){
const e = yield attempt(ajaxGet('/message'));
return S.either(
e => `Oh no! ${e}`,
x => `Yippee! ${x}`,
e
);
})
.fork(console.error, console.log);
//> "Oh no! Failed to load /message"
This function has an alias go, for environments in which do is a reserved word.
try :: Catchable e (() -> r) -> Future e rtry :: Catchable e (() -> r) -> Future e r
attempt :: Catchable e (() -> r) -> Future e r
Creates a Future which resolves with the result of calling the given function, or rejects with the error thrown by the given function.
Short for Future.encase(f, undefined).
const data = {foo: 'bar'};
Future.try(() => data.foo.bar.baz)
.fork(console.error, console.log);
//> [TypeError: Cannot read property 'baz' of undefined]
This function has an alias attempt, for environments in which try is a reserved word.
tryP :: (() -> Promise e r) -> Future e rtryP :: (() -> Promise e r) -> Future e r
Create a Future which when forked spawns a Promise using the given function and resolves with its resolution value, or rejects with its rejection reason.
Short for Future.encaseP(f, undefined).
Future.tryP(() => Promise.resolve('Hello'))
.fork(console.error, console.log);
//> "Hello"
node :: (Nodeback e r -> x) -> Future e rnode :: (Nodeback e r -> x) -> Future e r
Creates a Future which rejects with the first argument given to the function, or resolves with the second if the first is not present.
This is very similar to the Future()-constructor, except that it
takes a single function with two arguments instead of two functions with a
single argument.
Short for Future.encaseN(f, undefined).
Future.node(done => {
done(null, 'Hello');
})
.fork(console.error, console.log);
//> "Hello"
encase :: (Catchable e (a -> r)) -> a -> Future e rencase :: (Catchable e ((a ) -> r)) -> a -> Future e r
encase2 :: (Catchable e ((a, b ) -> r)) -> a -> b -> Future e r
encase3 :: (Catchable e ((a, b, c) -> r)) -> a -> b -> c -> Future e r
Takes a function and a value, and returns a Future which when forked calls the function with the value and resolves with the result. If the function throws an exception, it is caught and the Future will reject with the exception:
const data = '{"foo" = "bar"}';
Future.encase(JSON.parse, data)
.fork(console.error, console.log);
//! [SyntaxError: Unexpected token =]
Partially applying encase with a function f allows us to create a "safe"
version of f. Instead of throwing exceptions, the encased version always
returns a Future when given the remaining argument(s):
const data = '{"foo" = "bar"}';
const safeJsonParse = Future.encase(JSON.parse);
safeJsonParse(data).fork(console.error, console.log);
//! [SyntaxError: Unexpected token =]
Furthermore; encase2 and encase3 are binary and ternary versions of
encase, applying two or three arguments to the given function respectively.
encaseP :: ((a) -> Promise e r) -> a -> Future e rencaseP :: ((a) -> Promise e r) -> a -> Future e r
encaseP2 :: ((a, b) -> Promise e r) -> a -> b -> Future e r
encaseP3 :: ((a, b, c) -> Promise e r) -> a -> b -> c -> Future e r
Allows Promise-returning functions to be turned into Future-returning functions.
Takes a function which returns a Promise, and a value, and returns a Future. When forked, the Future calls the function with the value to produce the Promise, and resolves with its resolution value, or rejects with its rejection reason.
const fetchf = Future.encaseP(fetch);
fetchf('https://api.github.com/users/Avaq')
.chain(res => Future.tryP(_ => res.json()))
.map(user => user.name)
.fork(console.error, console.log);
//> "Aldwin Vlasblom"
Furthermore; encaseP2 and encaseP3 are binary and ternary versions
of encaseP, applying two or three arguments to the given function respectively.
encaseN :: ((a, Nodeback e r) -> x) -> a -> Future e rencaseN :: ((a, Nodeback e r) -> x) -> a -> Future e r
encaseN2 :: ((a, b, Nodeback e r) -> x) -> a -> b -> Future e r
encaseN3 :: ((a, b, c, Nodeback e r) -> x) -> a -> b -> c -> Future e r
Allows continuation-passing-style functions to be turned into Future-returning functions.
Takes a function which accepts as its last parameter a Nodeback, and a value, and returns a Future. When forked, the Future calls the function with the value and a Nodeback and resolves the second argument passed to the Nodeback, or or rejects with the first argument.
const fs = require('fs');
const read = Future.encaseN2(fs.readFile);
read('README.md', 'utf8')
.map(text => text.split('\n'))
.map(lines => lines[0])
.fork(console.error, console.log);
//> "# [](#butterfly)"
Furthermore; encaseN2 and encaseN3 are binary and ternary versions
of encaseN, applying two or three arguments to the given function respectively.
Future.chainRec :: ((a -> Next a, b -> Done b, a) -> Future e (Next a | Done b), a) -> Future e bFuture.chainRec :: ((a -> Next a, b -> Done b, a) -> Future e (Next a | Done b), a) -> Future e b
Implementation of Fantasy Land ChainRec. Since Fluture 6.0
introduced stack safety there should be no need to use this
function directly. Instead it's recommended to use chain(rec).
map :: Functor m => (a -> b) -> m a -> m bmap :: Functor m => (a -> b) -> m a -> m b
Future.map :: Functor m => (a -> b) -> m a -> m b
Par.map :: Functor m => (a -> b) -> m a -> m b
Future.prototype.map :: Future e a ~> (a -> b) -> Future e b
Transforms the resolution value inside the Future, and returns a new Future with
the transformed value. This is like doing promise.then(x => x + 1), except
that it's lazy, so the transformation will not be applied before the Future is
forked. The transformation is only applied to the resolution branch: If the
Future is rejected, the transformation is ignored. To learn more about the exact
behaviour of map, check out its spec.
Future.of(1)
.map(x => x + 1)
.fork(console.error, console.log);
//> 2
bimap :: Bifunctor m => (a -> c) -> (b -> d) -> m a b -> m c dbimap :: Bifunctor m => (a -> c) -> (b -> d) -> m a b -> m c d
Future.bimap :: Bifunctor m => (a -> c) -> (b -> d) -> m a b -> m c d
Future.prototype.bimap :: Future a b ~> (a -> c) -> (b -> d) -> Future c d
Maps the left function over the rejection value, or the right function over the resolution value, depending on which is present.
Future.of(1)
.bimap(x => x + '!', x => x + 1)
.fork(console.error, console.log);
//> 2
Future.reject('error')
.bimap(x => x + '!', x => x + 1)
.fork(console.error, console.log);
//> "error!"
chain :: Chain m => (a -> m b) -> m a -> m bchain :: Chain m => (a -> m b) -> m a -> m b
Future.chain :: Chain m => (a -> m b) -> m a -> m b
Future.prototype.chain :: Future e a ~> (a -> Future e b) -> Future e b
Allows the creation of a new Future based on the resolution value. This is like
doing promise.then(x => Promise.resolve(x + 1)), except that it's lazy, so the
new Future will not be created until the other one is forked. The function is
only ever applied to the resolution value; it's ignored when the Future was
rejected. To learn more about the exact behaviour of chain, check out its spec.
Future.of(1)
.chain(x => Future.of(x + 1))
.fork(console.error, console.log);
//> 2
swap :: Future a b -> Future b aswap :: Future a b -> Future b a
Future.prototype.swap :: Future a b ~> Future b a
Resolve with the rejection reason, or reject with the resolution value.
Future.of(new Error('It broke')).swap().fork(console.error, console.log);
//! [It broke]
Future.reject('Nothing broke').swap().fork(console.error, console.log);
//> "Nothing broke"
mapRej :: (a -> c) -> Future a b -> Future c bmapRej :: (a -> c) -> Future a b -> Future c b
Future.prototype.mapRej :: Future a b ~> (a -> c) -> Future c b
Map over the rejection reason of the Future. This is like map, but for the
rejection branch.
Future.reject(new Error('It broke!'))
.mapRej(err => new Error('Some extra info: ' + err.message))
.fork(console.error, console.log);
//! [Some extra info: It broke!]
chainRej :: (a -> Future c b) -> Future a b -> Future c bchainRej :: (a -> Future c b) -> Future a b -> Future c b
Future.prototype.chainRej :: Future a b ~> (a -> Future c b) -> Future c b
Chain over the rejection reason of the Future. This is like chain, but for
the rejection branch.
Future.reject(new Error('It broke!')).chainRej(err => {
console.error(err);
return Future.of('All is good');
})
.fork(console.error, console.log);
//> "All is good"
fold :: (a -> c) -> (b -> c) -> Future a b -> Future d cfold :: (a -> c) -> (b -> c) -> Future a b -> Future d c
Future.prototype.fold :: Future a b ~> (a -> c, b -> c) -> Future d c
Applies the left function to the rejection value, or the right function to the resolution value, depending on which is present, and resolves with the result.
This provides a convenient means to ensure a Future is always resolved. It can
be used with other type constructors, like S.Either, to maintain a
representation of failures:
Future.of('hello')
.fold(S.Left, S.Right)
.value(console.log);
//> Right('hello')
Future.reject('it broke')
.fold(S.Left, S.Right)
.value(console.log);
//> Left('it broke')
ap :: Apply m => m (a -> b) -> m a -> m bap :: Apply m => m (a -> b) -> m a -> m b
Future.ap :: Apply m => m (a -> b) -> m a -> m b
Par.ap :: Apply m => m (a -> b) -> m a -> m b
Future.prototype.ap :: Future e (a -> b) ~> Future e a -> Future e b
Applies the function contained in the left-hand Future or Apply to the value contained in the right-hand Future or Apply. If one of the Futures rejects the resulting Future will also be rejected.
Future.of(x => y => x + y)
.ap(Future.of(1))
.ap(Future.of(2))
.fork(console.error, console.log);
//> 3
Note that even though #ap does not conform to the latest spec,
the hidden fantasy-land/ap-method does. Therefore Future remains fully
compliant to Fantasy Land.
and :: Future a b -> Future a c -> Future a cand :: Future a b -> Future a c -> Future a c
Future.prototype.and :: Future a b ~> Future a c -> Future a c
Logical and for Futures.
Returns a new Future which either rejects with the first rejection reason, or resolves with the last resolution value once and if both Futures resolve. This behaves analogously to how JavaScript's and-operator does.
//An asynchronous version of:
//isResolved() && getValue();
isResolved().and(getValue());
//Asynchronous "all", where the resulting Future will be the leftmost to reject:
const all = ms => ms.reduce(Future.and, Future.of(true));
all([Future.after(20, 1), Future.of(2)]).value(console.log);
//> 2
or :: Future a b -> Future a b -> Future a bor :: Future a b -> Future a b -> Future a b
Future.prototype.or :: Future a b ~> Future a b -> Future a b
Logical or for Futures.
Returns a new Future which either resolves with the first resolution value, or rejects with the last rejection value once and if both Futures reject. This behaves analogously to how JavaScript's or-operator does.
//An asynchronous version of:
//planA() || planB();
planA().or(planB());
//Asynchronous "any", where the resulting Future will be the leftmost to resolve:
const any = ms => ms.reduce(Future.or, Future.reject('empty list'));
any([Future.reject(1), Future.after(20, 2), Future.of(3)]).value(console.log);
//> 2
fork :: (a -> x) -> (b -> x) -> Future a b -> Cancelfork :: (a -> x) -> (b -> x) -> Future a b -> Cancel
Future.prototype.fork :: Future a b ~> (a -> x, b -> x) -> Cancel
Execute the computation that was passed to the Future at construction
using the given reject and resolve callbacks.
Future.of('world').fork(
err => console.log(`Oh no! ${err.message}`),
thing => console.log(`Hello ${thing}!`)
);
//> "Hello world!"
Future.reject(new Error('It broke!')).fork(
err => console.log(`Oh no! ${err.message}`),
thing => console.log(`Hello ${thing}!`)
);
//> "Oh no! It broke!"
const consoleFork = Future.fork(console.error, console.log);
consoleFork(Future.of('Hello'));
//> "Hello"
After you fork a Future, the computation will start running. If you wish to
cancel the computation, you may use the function returned by fork:
const fut = Future.after(300, 'hello');
const cancel = fut.fork(console.error, console.log);
cancel();
//Nothing will happen. The Future was cancelled before it could settle.
value :: (b -> x) -> Future a b -> Cancelvalue :: (b -> x) -> Future a b -> Cancel
Future.prototype.value :: Future a b ~> (b -> x) -> Cancel
Extracts the value from a resolved Future by forking it. Only use this function
if you are sure the Future is going to be resolved, for example; after using
.fold(). If the Future rejects and value was used, an (likely uncatchable)
Error will be thrown.
Future.reject(new Error('It broke'))
.fold(S.Left, S.Right)
.value(console.log);
//> Left([Error: It broke])
Just like fork, value returns the Cancel function:
Future.after(300, 'hello').value(console.log)();
//Nothing will happen. The Future was cancelled before it could settle.
done :: Nodeback a b -> Future a b -> Canceldone :: Nodeback a b -> Future a b -> Cancel
Future.prototype.done :: Future a b ~> Nodeback a b -> Cancel
Fork the Future into a Nodeback.
Future.of('hello').done((err, val) => console.log(val));
//> "hello"
This is like fork, but instead of taking two unary functions, it takes
a single binary function. As with fork(), done() returns Cancel:
const m = Future.after(300, 'hello');
const cancel = m.done((err, val) => console.log(val));
cancel();
//Nothing will happen. The Future was cancelled before it could settle.
promise :: Future a b -> Promise b apromise :: Future a b -> Promise b a
Future.prototype.promise :: Future a b ~> Promise b a
An alternative way to fork the Future. This eagerly forks the Future and
returns a Promise of the result. This is useful if some API wants you to give it
a Promise. It's the only method which forks the Future without a forced way to
handle the rejection branch, so I recommend against using it for anything else.
Future.of('Hello').promise().then(console.log);
//> "Hello"
race :: Future a b -> Future a b -> Future a brace :: Future a b -> Future a b -> Future a b
Future.prototype.race :: Future a b ~> Future a b -> Future a b
Race two Futures against each other. Creates a new Future which resolves or rejects with the resolution or rejection value of the first Future to settle.
Future.after(100, 'hello')
.race(Future.after(50, 'bye'))
.fork(console.error, console.log);
//> "bye"
const first = futures => futures.reduce(Future.race, Future.never);
first([
Future.after(100, 'hello'),
Future.after(50, 'bye'),
Future.rejectAfter(25, 'nope')
])
.fork(console.error, console.log);
//! "nope"
both :: Future a b -> Future a c -> Future a (Pair b c)both :: Future a b -> Future a c -> Future a (Pair b c)
Future.prototype.both :: Future a b ~> Future a c -> Future a (Pair b c)
Run two Futures in parallel. Basically like calling
Future.parallel with exactly two Futures:
const a = Future.of('a');
const b = Future.of('b');
Future.both(a, b).fork(console.error, console.log);
//> ['a', 'b']
parallel :: PositiveInteger -> Array (Future a b) -> Future a (Array b)parallel :: PositiveInteger -> Array (Future a b) -> Future a (Array b)
Creates a Future which when forked runs all Futures in the given array in
parallel, ensuring no more than limit Futures are running at once.
const tenFutures = Array.from(Array(10).keys()).map(Future.after(20));
//Runs all Futures in sequence:
Future.parallel(1, tenFutures).fork(console.error, console.log);
//after about 200ms:
//> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
//Runs upto five Futures in parallel:
Future.parallel(5, tenFutures).fork(console.error, console.log);
//after about 40ms:
//> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
//Runs all Futures in parallel:
Future.parallel(Infinity, tenFutures).fork(console.error, console.log);
//after about 20ms:
//> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
If you want to settle all Futures, even if some may fail, you can use this in combination with fold:
const instableFutures = Array.from({length: 4}, (_, i) =>
Future.node(done => done(Math.random() > 0.75 ? 'failed' : null, i))
);
const stabalizedFutures = instableFutures.map(Future.fold(S.Left, S.Right));
Future.parallel(Infinity, stabalizedFutures).fork(console.error, console.log);
//> [ Right(0), Left("failed"), Right(2), Right(3) ]
The ConcurrentFuture type is the result of applying concurrify
to Future. It provides a mechanism for constructing a
Fantasy Land Alternative from a member of Future. This
allows Futures to benefit from the Alternative Interface, which includes
parallel ap, zero and alt.
The idea is that you can switch back and forth between Future and
ConcurrentFuture, using Par and seq, to get sequential or
concurrent behaviour respectively. It's a useful type to pass to abstractions
that don't know about Future-specific functions like parallel or
race, but do know how to operate on Apply and Alternative.
const {of, ap, sequence} = require('sanctuary');
const {Future, Par, seq} = require('fluture');
//Some dummy values
const x = 1;
const f = a => a + 1;
//The following two are equal ways to construct a ConcurrentFuture
const parx = of(Par, x);
const parf = Par(of(Future, f));
//We can make use of parallel apply
seq(ap(parx, parf)).value(console.log);
//> 2
//Or concurrent sequencing
seq(sequence(Par, [parx, parf])).value(console.log);
//> [x, f]
Converts a Future to a ConcurrentFuture.
Par :: Future a b -> ConcurrentFuture a bPar :: Future a b -> ConcurrentFuture a b
Constructs a ConcurrentFuture with the given resolution value.
Par.of :: b -> ConcurrentFuture a bPar.of :: b -> ConcurrentFuture a b
Constructs a ConcurrentFuture which will never resolve or reject with anything.
Par.zero :: () -> ConcurrentFuture a aPar.zero :: () -> ConcurrentFuture a a
Converts a ConcurrentFuture to a Future.
seq :: ConcurrentFuture a b -> Future a bseq :: ConcurrentFuture a b -> Future a b
Select one of two Alts. In terms of the ConcurrentFuture
type, this means racing the two against one another with the same
semantics as race.
alt :: Alt f => f a -> f a -> f aalt :: Alt f => f a -> f a -> f a
Par.alt :: Alt f => f a -> f a -> f a
import {Future, Par, seq, alt} from 'fluture';
seq(alt(Par.zero, Par.of(1))).value(console.log);
//> 1
seq(alt(Par(Future.after(20, 1)), Future.after(10, 2))).value(console.log);
//> 2
Functions listed under this category allow for more fine-grained control over the flow of acquired values.
hook :: Future a b -> (b -> Future a c) -> (b -> Future a d) -> Future a dhook :: Future a b -> (b -> Future a c) -> (b -> Future a d) -> Future a d
Allows a Future-returning function to be decorated with resource acquistion
and disposal. The signature is like hook(acquire, dispose, consume), where
acquire is a Future which might create connections, open file handlers, etc.
dispose is a function that takes the result from acquire and should be used
to clean up (close connections etc) and consume also takes the result from
acquire, and may be used to perform any arbitrary computations using the
resource. The resolution value of dispose is ignored.
const withConnection = Future.hook(
openConnection('localhost'),
closeConnection
);
withConnection(
conn => query(conn, 'EAT * cakes FROM bakery')
)
.fork(console.error, console.log);
In the case that a hooked Future is cancelled after the resource was acquired,
dispose will be executed and immediately cancelled. This means that rejections
which may happen during this disposal are silently ignored. To ensure that
resources are disposed during cancellation, you might synchronously dispose
resources in the cancel function of the disposal Future:
const closeConnection = conn => Future((rej, res) => {
//We try to dispose gracefully.
conn.flushGracefully(err => {
if(err === null){
conn.close();
res();
}else{
rej(err);
}
});
//On cancel, we force dispose.
return () => conn.close();
});
finally :: Future a c -> Future a b -> Future a bfinally :: Future a c -> Future a b -> Future a b
lastly :: Future a c -> Future a b -> Future a b
Future.prototype.finally :: Future a b ~> Future a c -> Future a b
Future.prototype.lastly :: Future a b ~> Future a c -> Future a b
Run a second Future after the first settles (successfully or unsuccessfully). Rejects with the rejection reason from the first or second Future, or resolves with the resolution value from the first Future.
Future.of('Hello')
.finally(Future.of('All done!').map(console.log))
.fork(console.error, console.log);
//> "All done!"
//> "Hello"
Note that the first Future is given as the last argument to Future.finally():
const program = S.pipe([
Future.of,
Future.finally(Future.of('All done!').map(console.log)),
Future.fork(console.error, console.log)
]);
program('Hello');
//> "All done!"
//> "Hello"
As with hook; when the Future is cancelled before the finally
computation is running, the finally computation is executed and immediately
cancelled.
This function has an alias lastly, for environments in which finally is a reserved word.
cache :: Future a b -> Future a bcache :: Future a b -> Future a b
Returns a Future which caches the resolution value of the given Future so that whenever it's forked, it can load the value from cache rather than reexecuting the chain.
const {readFile} = require('fs');
const eventualPackage = Future.cache(
Future.node(done => {
console.log('Reading some big data');
readFile('package.json', 'utf8', done);
})
);
eventualPackage.fork(console.error, console.log);
//> "Reading some big data"
//> "{...}"
eventualPackage.fork(console.error, console.log);
//> "{...}"
isFuture :: a -> BooleanisFuture :: a -> Boolean
Returns true for Futures and false for everything else. This function
(and S.is) also return true for instances of Future that were
created within other contexts. It is therefore recommended to use this over
instanceof, unless your intent is to explicitly check for Futures created
using the exact Future constructor you're testing against.
const Future1 = require('/path/to/fluture');
const Future2 = require('/other/path/to/fluture');
const noop = () => {};
const m1 = Future1(noop);
Future1.isFuture(m1) === (m1 instanceof Future1);
//> true
const m2 = Future2(noop);
Future1.isFuture(m2) === (m2 instanceof Future1);
//> false
never :: Future a anever :: Future a a
A Future that never settles. Can be useful as an initial value when reducing
with race, for example.
isNever :: a -> BooleanisNever :: a -> Boolean
Returns true if the given input is a never.
extractLeft :: Future a b -> Array aextractLeft :: Future a b -> Array a
Future.prototype.extractLeft :: Future a b ~> () -> Array a
Returns an array whose only element is the rejection reason of the Future. In many cases it will be impossible to extract this value; In those cases, the array will be empty. This function is meant to be used for type introspection: it is not the correct way to consume a Future.
extractRight :: Future a b -> Array bextractRight :: Future a b -> Array b
Future.prototype.extractRight :: Future a b ~> () -> Array b
Returns an array whose only element is the resolution value of the Future. In many cases it will be impossible to extract this value; In those cases, the array will be empty. This function is meant to be used for type introspection: it is not the correct way to consume a Future.
FAQs
FantasyLand compliant (monadic) alternative to Promises
The npm package fluture receives a total of 21,808 weekly downloads. As such, fluture popularity was classified as popular.
We found that fluture demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 3 open source maintainers collaborating on the project.
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