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# Play with Streams

Potentially infinite effectful streams!

## Stream

/**
* Stream represents a potentially infinite stream of effectful computations
* It is a more general structure in respect to the base effect
* that allows running computations in a rective manner
*/
export interface Stream<R, E, A> {}
/**
* Create a Stream from a source A action.
*
* The contract is that the acquisition of the resource should produce a Wave that may be repeatedly evaluated
* during the scope of the Managed
* If there is more data in the stream, the Wave should produce some(A) otherwise it should produce none.
* Once it produces none, it will not be evaluated again.
* @param r
*/
export function fromSource<R, E, A>(
r: Managed<R, E, T.Effect<R, E, Option<A>>>
): Stream<R, E, A>
/**
* Create a stream from an Array
* @param as
*/
export function fromArray<A>(as: readonly A[]): Stream<T.NoEnv, T.NoErr, A>
/**
* Create a stream from an iterator
* @param iter
*/
export function fromIterator<A>(
iter: Lazy<Iterator<A>>
): Stream<T.NoEnv, T.NoErr, A>
/**
* Create a stream that emits the elements in a range
* @param start
* @param interval
* @param end
*/
export function fromRange(
start: number,
interval?: number,
end?: number
): Stream<T.NoEnv, T.NoErr, number>
/**
* Create a stream from an existing iterator
* @param iter
*/
export function fromIteratorUnsafe<A>(
iter: Iterator<A>
): Stream<T.NoEnv, T.NoErr, A>
/**
* Create a stream that emits a single element
* @param a
*/
export function once<A>(a: A): Stream<T.NoEnv, T.NoErr, A>
/**
* Create a stream that emits As as fast as possible
*
* Be cautious when using this. If your entire pipeline is full of synchronous actions you can block the main
* thread until the stream runs to completion (or forever) using this
* @param a
*/
export function repeatedly<A>(a: A): Stream<T.NoEnv, T.NoErr, A>
export function periodically(ms: number): Stream<T.NoEnv, T.NoErr, number>
/**
* A stream that emits no elements an immediately terminates
*/
export const empty: Stream<
T.NoEnv,
T.NoErr,
never
>
/**
* Create a stream that evalutes w to emit a single element
* @param w
*/
export function encaseEffect<R, E, A>(w: T.Effect<R, E, A>): Stream<R, E, A>
/**
* Create a stream that immediately fails
* @param e
*/
export function raised<E>(e: E): Stream<T.NoEnv, E, never>
/**
* Create a stream that immediately aborts
* @param e
*/
export function aborted(e: unknown): Stream<T.NoEnv, T.NoErr, never>
/**
* Create a stream that immediately emits either 0 or 1 elements
* @param opt
*/
export function fromOption<A>(opt: Option<A>): Stream<T.NoEnv, T.NoErr, A>
/**
* Zip all stream elements with their index ordinals
* @param stream
*/
export function zipWithIndex<R, E, A>(
stream: Stream<R, E, A>
): Stream<R, E, readonly [A, number]>
/**
* Create a stream that emits all the elements of stream1 followed by all the elements of stream2
* @param stream1
* @param stream2
*/
export function concatL<R, E, A, R2, E2>(
stream1: Stream<R, E, A>,
stream2: Lazy<Stream<R2, E2, A>>
): Stream<R & R2, E | E2, A>
/**
* Strict form of concatL
* @param stream1
* @param stream2
*/
export function concat<R, E, A, R2, E2>(
stream1: Stream<R, E, A>,
stream2: Stream<R2, E2, A>
): Stream<R & R2, E | E2, A>
/**
* Creates a stream that repeatedly emits the elements of a stream forever.
*
* The elements are not cached, any effects required (i.e. opening files or sockets) are repeated for each cycle
* @param stream
*/
export function repeat<R, E, A>(stream: Stream<R, E, A>): Stream<R, E, A>
/**
* Map the elements of a stream
* @param stream
* @param f
*/
export function map<R, A, B>(
f: FunctionN<[A], B>
): <E>(stream: Stream<R, E, A>) => Stream<R, E, B>
/**
* Map every element emitted by stream to b
* @param stream
* @param b
*/
export function as<R, E, A, B>(stream: Stream<R, E, A>, b: B): Stream<R, E, B>
/**
* Filter the elements of a stream by a predicate
* @param stream
* @param f
*/
export function filter<R, E, A>(
stream: Stream<R, E, A>,
f: Predicate<A>
): Stream<R, E, A>
/**
* Curried form of filter
* @param f
*/
export function filterWith<A>(
f: Predicate<A>
): <R, E>(stream: Stream<R, E, A>) => Stream<R, E, A>
// filter and refine
export function filterRefineWith<A, B extends A>(
f: Refinement<A, B>
): <R, E>(stream: Stream<R, E, A>) => Stream<R, E, B>
/**
* Filter the stream so that only items that are not equal to the previous item emitted are emitted
* @param eq
*/
eq: Eq<A>
): <R, E>(stream: Stream<R, E, A>) => Stream<R, E, A>
/**
* Fold the elements of this stream together using an effect.
*
* The resulting stream will emit 1 element produced by the effectful fold
* @param stream
* @param f
* @param seed
*/
export function foldM<R, E, A, R2, E2, B>(
stream: Stream<R, E, A>,
f: FunctionN<[B, A], T.Effect<R2, E2, B>>,
seed: B
): Stream<R & R2, E | E2, B>
/**
* Fold the elements of a stream together purely
* @param stream
* @param f
* @param seed
*/
export function fold<R, E, A, B>(
stream: Stream<R, E, A>,
f: FunctionN<[B, A], B>,
seed: B
): Stream<R, E, B>
/**
* Scan across the elements the stream.
*
* This is like foldM but emits every intermediate seed value in the resulting stream.
* @param stream
* @param f
* @param seed
*/
export function scanM<R, E, A, B, R2, E2>(
stream: Stream<R, E, A>,
f: FunctionN<[B, A], T.Effect<R2, E2, B>>,
seed: B
): Stream<R & R2, E | E2, B>
/**
* Purely scan a stream
* @param stream
* @param f
* @param seed
*/
export function scan<R, E, A, B>(
stream: Stream<R, E, A>,
f: FunctionN<[B, A], B>,
seed: B
): Stream<R, E, B>
/**
* Monadic chain on a stream
* @param stream
* @param f
*/
export function chain<A, R2, E2, B>(
f: FunctionN<[A], Stream<R2, E2, B>>
): <R, E>(stream: Stream<R, E, A>) => Stream<R & R2, E | E2, B>
/**
* Flatten a stream of streams
* @param stream
*/
export function flatten<R, E, R2, E2, A>(
stream: Stream<R, E, Stream<R2, E2, A>>
): Stream<R & R2, E | E2, A>
/**
* Map each element of the stream effectfully
* @param stream
* @param f
*/
export function mapM<R, E, A, R2, E2, B>(
stream: Stream<R, E, A>,
f: FunctionN<[A], T.Effect<R2, E2, B>>
): Stream<R & R2, E | E2, B>
export function mapMWith<A, R2, E2, B>(
f: FunctionN<[A], T.Effect<R2, E2, B>>
): <R, E>(stream: Stream<R, E, A>) => Stream<R & R2, E | E2, B>
/**
* A stream that emits no elements but never terminates.
*/
export const never: Stream<T.NoEnv, T.NoErr, never>
/**
* Transduce a stream via a sink.
*
* This repeatedly run a sink to completion on the elements of the input stream and emits the result of each run
* Leftovers from a previous run are fed to the next run
*
* @param stream
* @param sink
*/
export function transduce<R, E, A, R2, E2, S, B>(
stream: Stream<R, E, A>,
sink: Sink<R2, E2, S, A, B>
): Stream<R & R2, E | E2, B>
/**
* Drop some number of elements from a stream
*
* Their effects to be produced still occur in the background
* @param stream
* @param n
*/
export function drop<R, E, A>(
stream: Stream<R, E, A>,
n: number
): Stream<R, E, A>
/**
* Curried form of drop
* @param n
*/
export function dropWith(
n: number
): <R, E, A>(stream: Stream<R, E, A>) => Stream<R, E, A> {
return stream => drop(stream, n);
}
/**
* Take some number of elements of a stream
* @param stream
* @param n
*/
export function take<R, E, A>(
stream: Stream<R, E, A>,
n: number
): Stream<R, E, A>
/**
* Take elements of a stream while a predicate holds
* @param stream
* @param pred
*/
export function takeWhile<R, E, A>(
stream: Stream<R, E, A>,
pred: Predicate<A>
): Stream<R, E, A>
/**
* Push a stream into a sink to produce the sink's result
* @param stream
* @param sink
*/
export function into<R, E, A, R2, E2, S, B>(
stream: Stream<R, E, A>,
sink: Sink<R, E2, S, A, B>
): T.Effect<R & R2, E | E2, B>
/**
* Push a stream into a sink to produce the sink's result
* @param stream
* @param managedSink
*/
export function intoManaged<R, E, A, S, B>(
stream: Stream<R, E, A>,
managedSink: Managed<R, E, Sink<R, E, S, A, B>>
): T.Effect<R, E, B>
/**
* Push a stream in a sink to produce the result and the leftover
* @param stream
* @param sink
*/
export function intoLeftover<R, E, A, S, B>(
stream: Stream<R, E, A>,
sink: Sink<R, E, S, A, B>
/**
* Zip two streams together termitating when either stream is exhausted
* @param as
* @param bs
* @param f
*/
export function zipWith<R, E, A, R2, E2, B, C>(
as: Stream<R, E, A>,
bs: Stream<R2, E2, B>,
f: FunctionN<[A, B], C>
): Stream<R & R2, E | E2, C>
/**
* zipWith to form tuples
* @param as
* @param bs
*/
export function zip<R, E, A, R2, E2, B>(
as: Stream<R, E, A>,
bs: Stream<R2, E2, B>
): Stream<R & R2, E | E2, readonly [A, B]>
/**
* Feed a stream into a sink to produce a value.
*
* Emits the value and a 'remainder' stream that includes the rest of the elements of the input stream.
* @param stream
* @param sink
*/
export function peel<R, E, A, S, B>(
stream: Stream<R, E, A>,
sink: Sink<R, E, S, A, B>
): Stream<R, E, readonly [B, Stream<R, E, A>]>
export function peelManaged<R, E, A, S, B>(
stream: Stream<R, E, A>,
managedSink: Managed<R, E, Sink<R, E, S, A, B>>
): Stream<R, E, readonly [B, Stream<R, E, A>]>
/**
* Create a stream that switches to emitting elements of the most recent input stream.
* @param stream
*/
export function switchLatest<R, E, A>(
stream: Stream<R, E, Stream<R, E, A>>
): Stream<R, E, A>
/**
* Create a stream that switches to emitting the elements of the most recent stream produced by applying f to the
* element most recently emitted
* @param stream
* @param f
*/
export function chainSwitchLatest<R, E, A, R2, E2, B>(
stream: Stream<R, E, A>,
f: FunctionN<[A], Stream<R2, E2, B>>
): Stream<R & R2, E | E2, B>
/**
* Merge a stream of streams into a single stream.
*
* This stream will run up to maxActive streams concurrently to produce values into the output stream.
* @param stream the input stream
* @param maxActive the maximum number of streams to hold active at any given time
* this controls how much active streams are able to collectively produce in the face of a slow downstream consumer
*/
export function merge<R, E, A>(
stream: Stream<R, E, Stream<R, E, A>>,
maxActive: number
): Stream<R, E, A>
export function chainMerge<R, E, A, B>(
stream: Stream<R, E, A>,
f: FunctionN<[A], Stream<R, E, B>>,
maxActive: number
): Stream<R, E, B>
export function mergeAll<R, E, A>(
streams: Array<Stream<R, E, A>>
): Stream<R, E, A>
/**
* Drop elements of the stream while a predicate holds
* @param stream
* @param pred
*/
export function dropWhile<R, E, A>(
stream: Stream<R, E, A>,
pred: Predicate<A>
): Stream<R, E, A>
/**
* Collect all the elements emitted by a stream into an array.
* @param stream
*/
export function collectArray<R, E, A>(
stream: Stream<R, E, A>
): T.Effect<R, E, A[]>
/**
* Evaluate a stream for its effects
* @param stream
*/
export function drain<R, E, A>(stream: Stream<R, E, A>): T.Effect<R, E, void>
// instances
export const stream: Monad3E<URI> = {
URI,
map: map_,
of: <R, E, A>(a: A): Stream<R, E, A> => (once(a) as any) as Stream<R, E, A>,
ap: <R, R2, E, E2, A, B>(
sfab: Stream<R, E, FunctionN<[A], B>>,
sa: Stream<R2, E2, A>
) => zipWith(sfab, sa, (f, a) => f(a)),
chain: chain_
} as const;
// encase a node js stream object readable into a stream
}
// encase a node js stream object readable into a stream (batched)
batch: number,
every: number
) {
}

## Sink

export interface Sink<R, E, S, A, B> {
readonly initial: T.Effect<R, E, SinkStep<A, S>>;
step: (state: S, next: A) => T.Effect<R, E, SinkStep<A, S>>;
extract: (step: S) => T.Effect<R, E, B>;
}
export interface SinkPure<S, A, B> {
step: (state: S, next: A) => SinkStep<A, S>;
extract: (state: S) => B;
}
/**
* Step a sink repeatedly.
* If the sink completes before consuming all of the input, then the done state will include the ops leftovers
* and anything left in the array
* @param sink
* @param s
* @param multi
*/
export function stepMany<R, E, S, A, B>(
sink: Sink<R, E, S, A, B>,
s: S,
): T.Effect<R, E, SinkStep<A, S>>
export function liftPureSink<S, A, B>(
sink: SinkPure<S, A, B>
): Sink<T.NoEnv, T.NoErr, S, A, B>
export function collectArraySink<R, E, A>(): Sink<R, E, A[], A, A[]>
export function drainSink<R, E, A>(): Sink<R, E, void, A, void>
/**
* A sink that consumes no input to produce a constant b
* @param b
*/
export function constSink<R, E, A, B>(b: B): Sink<R, E, void, A, B>
/**
* A sink that produces the head element of a stream (if any elements are emitted)
*/
export function headSink<R, E, A>(): Sink<R, E, Option<A>, A, Option<A>>
/**
* A sink that produces the last element of a stream (if any elements are emitted)
*/
export function lastSink<R, E, A>(): Sink<R, E, Option<A>, A, Option<A>>
/**
* A sink that evalutes an action for every element of a sink and produces no value
* @param f
*/
export function evalSink<R, E, A>(
f: FunctionN<[A], T.Effect<R, E, unknown>>
): Sink<R, E, void, A, void>
/**
* A sink that consumes elements for which a predicate does not hold.
*
* Returns the first element for which the predicate did hold if such an element is found.
* @param f
*/
export function drainWhileSink<R, E, A>(
f: Predicate<A>
): Sink<R, E, Option<A>, A, Option<A>>
/**
* A sink that offers elements into a concurrent queue
*
* @param queue
*/
export function queueSink<R, E, A>(
queue: ConcurrentQueue<A>
): Sink<R, E, void, A, void>
/**
* A sink that offers elements into a queue after wrapping them in an option.
*
* The sink will offer one final none into the queue when the stream terminates
* @param queue
*/
export function queueOptionSink<R, E, A>(
queue: ConcurrentQueue<Option<A>>
): Sink<R, E, void, A, void>
/**
* Map the output value of a sink
* @param sink
* @param f
*/
export function map<R, E, S, A, B, C>(
sink: Sink<R, E, S, A, B>,
f: FunctionN<[B], C>
): Sink<R, E, S, A, C>

## Usage

import { effect as T, stream as S } from "@matechs/effect";
import { pipe } from "fp-ts/lib/pipeable";
const program = pipe(
S.periodically(100),
S.chain(n =>
S.encaseEffect(
T.sync(() => {
console.log(`got: \${n}`);
return n + 1;
})
)
),
S.filterWith(n => n > 5)
);
T.runToPromise(S.collectArray(S.take(program, 10))).then(r => {
console.log(`elements: \${r.length}`);
});
const program2 = pipe(S.repeatedly(1), s =>
S.foldM(S.take(s, 100000), (acc, n) => T.sync(() => acc + n), 0)
);
T.runToPromise(S.collectArray(program2)).then(r => {
console.log(`fold: \${r[0]}`);
});
// prints
// fold: 100000
// got: 0
// got: 1
// got: 2
// got: 3
// got: 4
// got: 5
// got: 6
// got: 7
// got: 8
// got: 9
// got: 10
// got: 11
// got: 12
// got: 13
// got: 14
// elements: 10
Note that errors are final if not handled in place, if you want a non final implementation you may use a `Stream<R, never, Either<E,A>>` where you can manage how error is propagated.
An implementation of `StreamEither` will be provided in work in progress and will be added to the core.