<B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(
self: Stream<A, E, R>
) => Stream<A, E | E2, R2 | R>
<A, E, R, B, E2, R2>(
self: Stream<A, E, R>,
schedule: Schedule.Schedule<B, unknown, E2, R2>
): Stream<A, E | E2, R | R2>Repeats each element of the stream according to the provided schedule, including the original emission.
Example (Repeating stream elements)
import { Console, Effect, Schedule, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.make("A", "B", "C").pipe(
Stream.repeatElements(Schedule.recurs(1)),
Stream.runCollect
)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ "A", "A", "B", "B", "C", "C" ]sequencing
Source effect/Stream.ts:290844 lines
export const const repeatElements: {
<B, E2, R2>(
schedule: Schedule.Schedule<
B,
unknown,
E2,
R2
>
): <A, E, R>(
self: Stream<A, E, R>
) => Stream<A, E | E2, R2 | R>
<A, E, R, B, E2, R2>(
self: Stream<A, E, R>,
schedule: Schedule.Schedule<
B,
unknown,
E2,
R2
>
): Stream<A, E | E2, R | R2>
}
Repeats each element of the stream according to the provided schedule,
including the original emission.
Example (Repeating stream elements)
import { Console, Effect, Schedule, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.make("A", "B", "C").pipe(
Stream.repeatElements(Schedule.recurs(1)),
Stream.runCollect
)
yield* Console.log(values)
})
Effect.runPromise(program)
// Output: [ "A", "A", "B", "B", "C", "C" ]
repeatElements: {
<function (type parameter) B in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>B, function (type parameter) E2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2>(
schedule: Schedule.Schedule<B, unknown, E2, R2>(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) B in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>B, unknown, function (type parameter) E2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2>
): <function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>R>(self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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; <…;
}
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>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | 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>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>E | function (type parameter) E2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <B, E2, R2>(schedule: Schedule.Schedule<B, unknown, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2 | function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>R>
<function (type parameter) A in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) B in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>B, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2>(
self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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; <…;
}
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, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R>,
schedule: Schedule.Schedule<B, unknown, E2, R2>(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) B in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>B, unknown, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2>
): 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, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2>
} = dual<(...args: Array<any>) => any, <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>) => Stream<A, E | E2, R | R2>>(arity: 2, body: <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>) => Stream<A, E | E2, R | R2>): ((...args: Array<any>) => any) & (<A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>) => Stream<A, E | E2, R | R2>) (+1 overload)Creates a function that can be called in data-first style or data-last
(pipe-friendly) style.
When to use
Use to expose one implementation through both direct and pipe-friendly
call styles.
Details
Pass either the arity of the uncurried function or a predicate that decides
whether the current call is data-first. Arity is the common case. Use a
predicate when optional arguments make arity ambiguous.
Example (Selecting data-first or data-last style by arity)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(2, (self, that) => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Defining overloads with call signatures)
import { Function, pipe } from "effect"
const sum: {
(that: number): (self: number) => number
(self: number, that: number): number
} = Function.dual(2, (self: number, that: number): number => self + that)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
Example (Selecting data-first or data-last style with a predicate)
import { Function, pipe } from "effect"
const sum = Function.dual<
(that: number) => (self: number) => number,
(self: number, that: number) => number
>(
(args) => args.length === 2,
(self, that) => self + that
)
console.log(sum(2, 3)) // 5
console.log(pipe(2, sum(3))) // 5
dual(
2,
<function (type parameter) A in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) B in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>B, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2>(
self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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; <…;
}
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, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R>,
schedule: Schedule.Schedule<B, unknown, E2, R2>(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) B in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>B, unknown, function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2>
): 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, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2> =>
const fromChannel: <
Arr extends Arr.NonEmptyReadonlyArray<any>,
E,
R
>(
channel: Channel.Channel<
Arr,
E,
void,
unknown,
unknown,
unknown,
R
>
) => Stream<
Arr extends Arr.NonEmptyReadonlyArray<infer A>
? A
: never,
E,
R
>
Creates a stream from a array-emitting Channel.
Example (Creating a stream from an array-emitting channel)
import { Channel, Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const channel = Channel.succeed([1, 2, 3] as const)
const stream = Stream.fromChannel(channel)
const result = yield* Stream.runCollect(stream)
yield* Console.log(result)
})
// Output: [ 1, 2, 3 ]
fromChannel(import ChannelChannel.const fromTransform: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
EX,
EnvX,
Env
>(
transform: (
upstream: Pull.Pull<InElem, InErr, InDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem, OutErr, OutDone, EnvX>,
EX,
Env
>
) => Channel<
OutElem,
Pull.ExcludeDone<OutErr> | EX,
OutDone,
InElem,
InErr,
InDone,
Env | EnvX
>
Creates a Channel from a transformation function that operates on upstream pulls.
Example (Creating channels from transforms)
import { Channel, Effect } from "effect"
const channel = Channel.fromTransform((upstream, scope) =>
Effect.succeed(upstream)
)
fromTransform((upstream: Pull.Pull<
unknown,
unknown,
unknown,
never
>
(parameter) upstream: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
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 ChannelChannel.const toTransform: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
channel: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => (
upstream: Pull.Pull<InElem, InErr, InDone>,
scope: Scope.Scope
) => Effect.Effect<
Pull.Pull<OutElem, OutErr, OutDone>,
never,
Env
>
Converts a Channel back to its underlying transformation function.
Example (Extracting channel transforms)
import { Channel } from "effect"
const channel = Channel.succeed(42)
const transform = Channel.toTransform(channel)
// transform can now be used directly
toTransform(import ChannelChannel.const flattenArray: <
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
ReadonlyArray<OutElem>,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
Flattens a channel that outputs arrays into a channel that outputs individual elements.
Example (Flattening arrays of channel output)
import { Channel, Data } from "effect"
class FlattenError extends Data.TaggedError("FlattenError")<{
readonly message: string
}> {}
// Create a channel that outputs arrays
const arrayChannel = Channel.fromIterable([
[1, 2, 3],
[4, 5],
[6, 7, 8, 9]
])
// Flatten the arrays into individual elements
const flattenedChannel = Channel.flattenArray(arrayChannel)
// Outputs: 1, 2, 3, 4, 5, 6, 7, 8, 9
flattenArray(self: Stream<A, E, R>(parameter) self: {
channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>;
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; <…;
}
Stream<A, E, R>.channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>(property) Stream<A, E, R>.channel: {
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; <…;
}
upstream: Pull.Pull<
unknown,
unknown,
unknown,
never
>
(parameter) upstream: {
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;
}
scope: Scope.Scope(parameter) scope: {
strategy: "sequential" | "parallel";
state: State.Open | State.Closed | State.Empty;
}
pullElement: Pull.Pull<A, E, void, never>(parameter) pullElement: {
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;
}
let pullRepeat:
| Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E | E2,
void,
R | R2
>
| undefined
import PullPull.interface Pull<out A, out E = never, out Done = void, out R = never>An effectful pull step that either produces a value, fails with E, or
signals completion with Cause.Done<Done>.
When to use
Use to model one low-level pull step when a consumer repeatedly evaluates an
effect that may emit a value, fail normally, or signal normal completion
through Cause.Done.
Details
Pull represents completion in the error channel so low-level stream
consumers can distinguish ordinary failures from end-of-input and carry a
leftover value when needed.
Pull<import ArrArr.type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A>, function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E2, void, function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2> | undefined = var undefinedundefined
const const pull: Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
R | R2
>
const pull: {
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 PullPull.interface Pull<out A, out E = never, out Done = void, out R = never>An effectful pull step that either produces a value, fails with E, or
signals completion with Cause.Done<Done>.
When to use
Use to model one low-level pull step when a consumer repeatedly evaluates an
effect that may emit a value, fail normally, or signal normal completion
through Cause.Done.
Details
Pull represents completion in the error channel so low-level stream
consumers can distinguish ordinary failures from end-of-input and carry a
leftover value when needed.
Pull<
import ArrArr.type NonEmptyReadonlyArray<A> = readonly [
A,
...A[]
]
A readonly array guaranteed to have at least one element.
When to use
Use when non-emptiness must be tracked at the type level while preventing mutation.
Many Array module functions accept or return this type.
Example (Typing a non-empty array)
import type { Array } from "effect"
const nonEmpty: Array.NonEmptyReadonlyArray<number> = [1, 2, 3]
const head: number = nonEmpty[0] // guaranteed to exist
NonEmptyReadonlyArray<function (type parameter) A in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>A>,
function (type parameter) E in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>E,
void,
function (type parameter) R in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, B, E2, R2>(self: Stream<A, E, R>, schedule: Schedule.Schedule<B, unknown, E2, R2>): Stream<A, E | E2, R | R2>R2
> = import EffectEffect.const gen: {
<Eff extends Effect<any, any, any>, AEff>(
f: () => Generator<Eff, AEff, never>
): Effect<
AEff,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer E, infer _R>
]
? E
: never,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer _E, infer R>
]
? R
: never
>
<Self, Eff extends Effect<any, any, any>, AEff>(
options: { readonly self: Self },
f: (this: Self) => Generator<Eff, AEff, never>
): Effect<
AEff,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer E, infer _R>
]
? E
: never,
[Eff] extends [never]
? never
: [Eff] extends [
Effect<infer _A, infer _E, infer R>
]
? R
: never
>
}
const element: Aelement = yield* pullElement: Pull.Pull<A, E, void, never>(parameter) pullElement: {
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 chunk: [A, ...A[]]const chunk: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => A | undefined;
push: (...items: Array<A>) => number;
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
reverse: () => Array<A>;
shift: () => A | undefined;
slice: (start?: number, end?: number) => Array<A>;
sort: (compareFn?: ((a: A, b: A) => number) | undefined) => [A, ...A[]];
splice: { (start: number, deleteCount?: number): Array<A>; (start: number, deleteCount: number, ...items: Array<A>): Array<A> };
unshift: (...items: Array<A>) => number;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): this is S[]; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: Array<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: Array<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
find: { (predicate: (value: A, index: number, obj: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any) => number;
fill: (value: A, start?: number, end?: number) => [A, ...A[]];
copyWithin: (target: number, start: number, end?: number) => [A, ...A[]];
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
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(const element: Aelement)
const const step: (
input: unknown
) => Pull.Pull<B, E2, B, R2>
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<B, unknown, E2, R2>(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; <…;
}
let pullRepeat:
| Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E | E2,
void,
R | R2
>
| undefined
const step: (
input: unknown
) => Pull.Pull<B, E2, B, R2>
const element: Aelement).Pipeable.pipe<Pull.Pull<B, E2, B, R2>, Effect.Effect<[A, ...A[]], E2 | Cause.Done<B>, R2>, Effect.Effect<readonly [A, ...A[]] | [A, ...A[]], Cause.Done<void> | E | Exclude<E2, Cause.Done<any>>, R | R2>>(this: Pull.Pull<...>, ab: (_: Pull.Pull<B, E2, B, R2>) => Effect.Effect<[A, ...A[]], E2 | Cause.Done<B>, R2>, bc: (_: Effect.Effect<[A, ...A[]], E2 | Cause.Done<B>, R2>) => Effect.Effect<readonly [A, ...A[]] | [...], Cause.Done<...> | ... 1 more ... | Exclude<...>, R | R2>): Effect.Effect<...> (+21 overloads)pipe(
import EffectEffect.const as: {
<B>(value: B): <A, E, R>(
self: Effect<A, E, R>
) => Effect<B, E, R>
<A, E, R, B>(
self: Effect<A, E, R>,
value: B
): Effect<B, E, R>
}
const chunk: [A, ...A[]]const chunk: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => A | undefined;
push: (...items: Array<A>) => number;
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
reverse: () => Array<A>;
shift: () => A | undefined;
slice: (start?: number, end?: number) => Array<A>;
sort: (compareFn?: ((a: A, b: A) => number) | undefined) => [A, ...A[]];
splice: { (start: number, deleteCount?: number): Array<A>; (start: number, deleteCount: number, ...items: Array<A>): Array<A> };
unshift: (...items: Array<A>) => number;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): this is S[]; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: Array<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: Array<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
find: { (predicate: (value: A, index: number, obj: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any) => number;
fill: (value: A, start?: number, end?: number) => [A, ...A[]];
copyWithin: (target: number, start: number, end?: number) => [A, ...A[]];
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
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>
}
_: B | Cause.Done.Extract<E2>_) => {
let pullRepeat:
| Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E | E2,
void,
R | R2
>
| undefined
var undefinedundefined
return const pull: Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
R | R2
>
const pull: {
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 chunk: [A, ...A[]]const chunk: {
0: A;
length: number;
toString: () => string;
toLocaleString: { (): string; (locales: string | string[], options?: Intl.NumberFormatOptions & Intl.DateTimeFormatOptions): string };
pop: () => A | undefined;
push: (...items: Array<A>) => number;
concat: { (...items: Array<ConcatArray<A>>): Array<A>; (...items: Array<A | ConcatArray<A>>): Array<A> };
join: (separator?: string) => string;
reverse: () => Array<A>;
shift: () => A | undefined;
slice: (start?: number, end?: number) => Array<A>;
sort: (compareFn?: ((a: A, b: A) => number) | undefined) => [A, ...A[]];
splice: { (start: number, deleteCount?: number): Array<A>; (start: number, deleteCount: number, ...items: Array<A>): Array<A> };
unshift: (...items: Array<A>) => number;
indexOf: (searchElement: A, fromIndex?: number) => number;
lastIndexOf: (searchElement: A, fromIndex?: number) => number;
every: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): this is S[]; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): boolean };
some: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => boolean;
forEach: (callbackfn: (value: A, index: number, array: Array<A>) => void, thisArg?: any) => void;
map: (callbackfn: (value: A, index: number, array: Array<A>) => U, thisArg?: any) => Array<U>;
filter: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): Array<S>; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): Array<A> };
reduce: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
reduceRight: { (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A): A; (callbackfn: (previousValue: A, currentValue: A, currentIndex: number, array: Array<A>) => A, initialValue: A): A; (callbackfn: (previousVa…;
find: { (predicate: (value: A, index: number, obj: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any): A | undefined };
findIndex: (predicate: (value: A, index: number, obj: Array<A>) => unknown, thisArg?: any) => number;
fill: (value: A, start?: number, end?: number) => [A, ...A[]];
copyWithin: (target: number, start: number, end?: number) => [A, ...A[]];
entries: () => ArrayIterator<[number, A]>;
keys: () => ArrayIterator<number>;
values: () => ArrayIterator<A>;
includes: (searchElement: A, fromIndex?: number) => boolean;
flatMap: (callback: (this: This, value: A, index: number, array: Array<A>) => U | ReadonlyArray<U>, thisArg?: This | undefined) => Array<U>;
flat: (this: A, depth?: D | undefined) => Array<FlatArray<A, D>>;
at: (index: number) => A | undefined;
findLast: { (predicate: (value: A, index: number, array: Array<A>) => value is S, thisArg?: any): S | undefined; (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any): A | undefined };
findLastIndex: (predicate: (value: A, index: number, array: Array<A>) => unknown, thisArg?: any) => number;
toReversed: () => Array<A>;
toSorted: (compareFn?: ((a: A, b: A) => number) | undefined) => Array<A>;
toSpliced: { (start: number, deleteCount: number, ...items: Array<A>): Array<A>; (start: number, deleteCount?: number): Array<A> };
with: (index: number, value: A) => Array<A>;
}
import EffectEffect.const suspend: <A, E, R>(
effect: LazyArg<Effect<A, E, R>>
) => Effect<A, E, R>
Creates an Effect lazily, delaying construction until it is needed.
When to use
Use when you need to defer the evaluation of an effect until it is required.
Details
suspend takes a thunk that represents an effect and delays creating it
until the suspended effect is evaluated. This is useful for optimizing
expensive computations, managing circular dependencies such as recursive
functions, and helping TypeScript unify return types when branches construct
different effects. Any side effects or scoped captures inside the thunk are
re-executed on each invocation.
Example (Lazily evaluating side effects)
import { Effect } from "effect"
let i = 0
const bad = Effect.succeed(i++)
const good = Effect.suspend(() => Effect.succeed(i++))
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(bad)) // Output: 0
console.log(Effect.runSync(good)) // Output: 1
console.log(Effect.runSync(good)) // Output: 2
Example (Suspending recursive Fibonacci evaluation)
import { Effect } from "effect"
const blowsUp = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(blowsUp(n - 1), blowsUp(n - 2), (a, b) => a + b)
// console.log(Effect.runSync(blowsUp(32)))
// crash: JavaScript heap out of memory
const allGood = (n: number): Effect.Effect<number> =>
n < 2
? Effect.succeed(1)
: Effect.zipWith(
Effect.suspend(() => allGood(n - 1)),
Effect.suspend(() => allGood(n - 2)),
(a, b) => a + b
)
console.log(Effect.runSync(allGood(32)))
// Output: 3524578
Example (Helping TypeScript infer recursive effect types)
import { Effect } from "effect"
// Without suspend, TypeScript may struggle with type inference.
// Inferred type:
// (a: number, b: number) =>
// Effect<never, Error, never> | Effect<number, never, never>
const withoutSuspend = (a: number, b: number) =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
// Using suspend to unify return types.
// Inferred type:
// (a: number, b: number) => Effect<number, Error, never>
const withSuspend = (a: number, b: number) =>
Effect.suspend(() =>
b === 0
? Effect.fail(new Error("Cannot divide by zero"))
: Effect.succeed(a / b)
)
suspend(() => let pullRepeat:
| Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E | E2,
void,
R | R2
>
| undefined
const pull: Pull.Pull<
Arr.NonEmptyReadonlyArray<A>,
E,
void,
R | R2
>
const pull: {
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;
}