<A, E, R>(effect: Effect.Effect<A, E, R>): Stream<
A,
Pull.ExcludeDone<E>,
R
>Creates a stream from an effect producing a value of type A which repeats forever.
Example (Repeating an effect forever)
import { Console, Effect, Random, Stream } from "effect"
const program = Effect.gen(function*() {
const stream = Stream.fromEffectRepeat(Random.nextInt).pipe(
Stream.take(5)
)
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 3891571149, 4239494205, 2352981603, 2339111046, 1488052210 ]export const const fromEffectRepeat: <A, E, R>(
effect: Effect.Effect<A, E, R>
) => Stream<A, Pull.ExcludeDone<E>, R>
Creates a stream from an effect producing a value of type A which repeats forever.
Example (Repeating an effect forever)
import { Console, Effect, Random, Stream } from "effect"
const program = Effect.gen(function*() {
const stream = Stream.fromEffectRepeat(Random.nextInt).pipe(
Stream.take(5)
)
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 3891571149, 4239494205, 2352981603, 2339111046, 1488052210 ]
fromEffectRepeat = <function (type parameter) A in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>A, function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>E, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>R>(effect: Effect.Effect<A, E, R>(parameter) effect: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
import EffectEffect.interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>A, function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>E, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>R>): interface Stream<out A, out E = never, out R = never>A Stream<A, E, R> describes a program that can emit many A values, fail
with E, and require R.
Details
Streams are pull-based with backpressure and emit chunks to amortize effect
evaluation. They support monadic composition and error handling similar to
Effect, adapted for multiple values.
Example (Creating and consuming streams)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
yield* Stream.make(1, 2, 3).pipe(
Stream.map((n) => n * 2),
Stream.runForEach((n) => Console.log(n))
)
})
Effect.runPromise(program)
// Output:
// 2
// 4
// 6
Stream<function (type parameter) A in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>A, import PullPull.type ExcludeDone<E> =
E extends Cause.Done<any> ? never : E
Excludes Cause.Done completion signals from an error type union.
When to use
Use to describe the ordinary error type that remains after Cause.Done
completion signals have been handled or filtered out of an error union.
ExcludeDone<function (type parameter) E in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>E>, function (type parameter) R in <A, E, R>(effect: Effect.Effect<A, E, R>): Stream<A, Pull.ExcludeDone<E>, R>R> =>
const fromPull: <A, E, R, EX, RX>(
pull: Effect.Effect<
Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
R
>,
EX,
RX
>
) => Stream<A, Pull.ExcludeDone<E> | EX, R | RX>
Creates a stream from a pull effect, such as one produced by Stream.toPull.
Details
A pull effect yields chunks on demand and completes when the upstream stream ends.
See Stream.toPull for a matching producer.
Example (Creating a stream from a pull effect)
import { Console, Effect, Stream } from "effect"
const program = Effect.scoped(
Effect.gen(function*() {
const source = Stream.make(1, 2, 3)
const pull = yield* Stream.toPull(source)
const stream = Stream.fromPull(Effect.succeed(pull))
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
)
Effect.runPromise(program)
// Output: [1, 2, 3]
fromPull(import EffectEffect.const succeed: <A>(value: A) => Effect<A>Creates an Effect that always succeeds with a given value.
When to use
Use when an effect should complete successfully with a specific value without any errors
or external dependencies.
Example (Creating a successful effect)
import { Effect } from "effect"
// Creating an effect that represents a successful scenario
//
// ┌─── Effect<number, never, never>
// ▼
const success = Effect.succeed(42)
succeed(import EffectEffect.const map: {
<A, B>(f: (a: A) => B): <E, R>(
self: Effect<A, E, R>
) => Effect<B, E, R>
<A, E, R, B>(
self: Effect<A, E, R>,
f: (a: A) => B
): Effect<B, E, R>
}
effect: Effect.Effect<A, E, R>(parameter) effect: {
pipe: { <A>(this: A): A; <A, B = never>(this: A, ab: (_: A) => B): B; <A, B = never, C = never>(this: A, ab: (_: A) => B, bc: (_: B) => C): C; <A, B = never, C = never, D = never>(this: A, ab: (_: A) => B, bc: (_: B) => C, cd: (_: C) => D): D; <…;
toString: () => string;
toJSON: () => unknown;
}
import ArrArr.const of: <A>(a: A) => NonEmptyArray<A>Wraps a single value in a NonEmptyArray.
Example (Creating a single-element array)
import { Array } from "effect"
console.log(Array.of(1)) // [1]
of)))