<A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>Creates a stream from an effect producing an iterable of values.
When to use
Use when the iterable must be acquired from an Effect before the stream emits, and acquisition services or failures should be part of the stream.
Example (Creating a stream from an iterable effect)
import { Console, Context, Effect, Stream } from "effect"
class UserRepo extends Context.Service<UserRepo, {
readonly list: Effect.Effect<ReadonlyArray<string>>
}>()("UserRepo") {}
const listUsers = Effect.service(UserRepo).pipe(
Effect.andThen((repo) => repo.list)
)
const stream = Stream.fromIterableEffect(listUsers)
const program = Effect.gen(function*() {
const users = yield* stream.pipe(
Stream.provideService(UserRepo, {
list: Effect.succeed(["user1", "user2"])
}),
Stream.runCollect
)
yield* Console.log(users)
})
Effect.runPromise(program)
// Output: [ "user1", "user2" ]export const const fromIterableEffect: <A, E, R>(
iterable: Effect.Effect<Iterable<A>, E, R>
) => Stream<A, E, R>
Creates a stream from an effect producing an iterable of values.
When to use
Use when the iterable must be acquired from an Effect before the stream emits,
and acquisition services or failures should be part of the stream.
Example (Creating a stream from an iterable effect)
import { Console, Context, Effect, Stream } from "effect"
class UserRepo extends Context.Service<UserRepo, {
readonly list: Effect.Effect<ReadonlyArray<string>>
}>()("UserRepo") {}
const listUsers = Effect.service(UserRepo).pipe(
Effect.andThen((repo) => repo.list)
)
const stream = Stream.fromIterableEffect(listUsers)
const program = Effect.gen(function*() {
const users = yield* stream.pipe(
Stream.provideService(UserRepo, {
list: Effect.succeed(["user1", "user2"])
}),
Stream.runCollect
)
yield* Console.log(users)
})
Effect.runPromise(program)
// Output: [ "user1", "user2" ]
fromIterableEffect = <function (type parameter) A in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>A, function (type parameter) E in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>E, function (type parameter) R in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>R>(iterable: Effect.Effect<Iterable<A>, E, R>(parameter) iterable: {
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<interface Iterable<T, TReturn = any, TNext = any>Iterable<function (type parameter) A in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>A>, function (type parameter) E in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>E, function (type parameter) R in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, 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>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>A, function (type parameter) E in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>E, function (type parameter) R in <A, E, R>(iterable: Effect.Effect<Iterable<A>, E, R>): Stream<A, E, R>R> =>
const unwrap: <A, E2, R2, E, R>(
effect: Effect.Effect<Stream<A, E2, R2>, E, R>
) => Stream<
A,
E | E2,
R2 | Exclude<R, Scope.Scope>
>
Creates a stream produced from an Effect.
Example (Unwrapping a stream effect)
import { Console, Effect, Stream } from "effect"
const effect = Effect.succeed(Stream.make(1, 2, 3))
const stream = Stream.unwrap(effect)
const program = Effect.gen(function*() {
const chunk = yield* Stream.runCollect(stream)
yield* Console.log(chunk)
})
// [1, 2, 3]
unwrap(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>
}
iterable: Effect.Effect<Iterable<A>, E, R>(parameter) iterable: {
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;
}
const fromIterable: <A>(
iterable: Iterable<A>,
options?: {
readonly chunkSize?: number | undefined
}
) => Stream<A>
Creates a new Stream from an iterable collection of values.
Details
chunkSize: Maximum number of values emitted per chunk.
Example (Creating a stream from an iterable)
import { Console, Effect, Stream } from "effect"
const numbers = [1, 2, 3]
const program = Effect.gen(function*() {
const stream = Stream.fromIterable(numbers)
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 1, 2, 3 ]
fromIterable))