<O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>Creates a stream that emits each output of a schedule that does not require input, for as long as the schedule continues.
Example (Creating a stream from a schedule)
import { Console, Effect, Schedule, Stream } from "effect"
const program = Effect.gen(function*() {
const schedule = Schedule.spaced("50 millis").pipe(
Schedule.upTo({ times: 3 })
)
const stream = Stream.fromSchedule(schedule)
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 0, 1, 2 ]constructors
Source effect/Stream.ts:14887 lines
export const const fromSchedule: <O, E, R>(
schedule: Schedule.Schedule<O, unknown, E, R>
) => Stream<O, E, R>
Creates a stream that emits each output of a schedule that does not require input,
for as long as the schedule continues.
Example (Creating a stream from a schedule)
import { Console, Effect, Schedule, Stream } from "effect"
const program = Effect.gen(function*() {
const schedule = Schedule.spaced("50 millis").pipe(
Schedule.upTo({ times: 3 })
)
const stream = Stream.fromSchedule(schedule)
const values = yield* Stream.runCollect(stream)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ 0, 1, 2 ]
fromSchedule = <function (type parameter) O in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>O, function (type parameter) E in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>E, function (type parameter) R in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>R>(schedule: Schedule.Schedule<O, unknown, E, R>(parameter) schedule: {
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; <…;
}
import ScheduleSchedule.interface Schedule<out Output, in Input = unknown, out Error = never, out Env = never>A Schedule defines a strategy for repeating or retrying effects based on some policy.
Example (Defining retry and repeat schedules)
import { Console, Data, Effect, Schedule } from "effect"
class NetworkError extends Data.TaggedError("NetworkError")<{
readonly attempt: number
}> {}
// Basic retry schedule - retry up to 3 times with exponential backoff
const retrySchedule = Schedule.max([
Schedule.exponential("100 millis"),
Schedule.recurs(3)
])
// Basic repeat schedule - repeat every 30 seconds forever
const repeatSchedule: Schedule.Schedule<number, unknown, never> = Schedule
.spaced("30 seconds")
const program = Effect.gen(function*() {
let attempts = 0
const result1 = yield* Effect.retry(
Effect.gen(function*() {
attempts++
if (attempts < 3) {
return yield* Effect.fail(new NetworkError({ attempt: attempts }))
}
return "Success"
}),
retrySchedule
)
console.log(result1) // "Success"
yield* Console.log("heartbeat").pipe(
Effect.repeat(repeatSchedule.pipe(Schedule.upTo({ times: 5 })))
)
})
The Schedule namespace contains types and utilities for working with schedules.
Schedule<function (type parameter) O in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>O, unknown, function (type parameter) E in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>E, function (type parameter) R in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, 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) O in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>O, function (type parameter) E in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, E, R>E, function (type parameter) R in <O, E, R>(schedule: Schedule.Schedule<O, unknown, E, R>): Stream<O, 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 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>
}
import ScheduleSchedule.const toStepWithSleep: <
Output,
Input,
Error,
Env
>(
schedule: Schedule<Output, Input, Error, Env>
) => Effect<
(
input: Input
) => Pull.Pull<Output, Error, Output, Env>,
never,
Env
>
Extracts a step function from a Schedule that automatically handles sleep delays.
Example (Extracting a sleeping step function)
import { Effect, Schedule } from "effect"
// Convert schedule to step function with automatic sleeping
const schedule = Schedule.spaced("1 second").pipe(Schedule.upTo({ times: 3 }))
const program = Effect.gen(function*() {
const stepWithSleep = yield* Schedule.toStepWithSleep(schedule)
// Each call will automatically sleep for the scheduled delay
console.log("Starting...")
const result1 = yield* stepWithSleep("first")
console.log(`First result: ${result1}`)
const result2 = yield* stepWithSleep("second")
console.log(`Second result: ${result2}`)
const result3 = yield* stepWithSleep("third")
console.log(`Third result: ${result3}`)
})
toStepWithSleep(schedule: Schedule.Schedule<O, unknown, E, R>(parameter) schedule: {
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; <…;
}
step: (
input: unknown
) => Pull.Pull<O, E, O, R>
import PullPull.const catchDone: {
<E, A2, E2, R2>(
f: (
leftover: Cause.Done.Extract<E>
) => Effect<A2, E2, R2>
): <A, R>(
self: Effect<A, E, R>
) => Effect<A | A2, ExcludeDone<E> | E2, R | R2>
<A, R, E, A2, E2, R2>(
self: Effect<A, E, R>,
f: (
leftover: Cause.Done.Extract<E>
) => Effect<A2, E2, R2>
): Effect<A | A2, ExcludeDone<E> | E2, R | R2>
}
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>
}
step: (
input: unknown
) => Pull.Pull<O, E, O, R>
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), () => import CauseCause.const done: <A = void>(
value?: A
) => Effect.Effect<never, Done<A>>
Creates an Effect that fails with a Done error. Shorthand for
Effect.fail(Cause.Done(value)).
When to use
Use when you model stream or queue completion through the error channel.
Example (Failing with Done)
import { Cause, Effect } from "effect"
const program = Cause.done("finished")
Effect.runPromiseExit(program).then((exit) => {
console.log(exit._tag) // "Failure"
})
done())
)
)