<A2, E2, R2, S, E, A, A3, E3, R3>(
that: Stream<A2, E2, R2>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>
<A, E, R, A2, E2, R2, S, A3, E3, R3>(
self: Stream<A, E, R>,
that: Stream<A2, E2, R2>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
): Stream<A3, E3, R | R2 | R3>Combines elements from this stream and the specified stream by repeatedly applying a stateful function that can pull from either side.
Details
Where possible, prefer Stream.combineArray for a more efficient
implementation.
Example (Combining streams with state)
import { Console, Effect, Stream } from "effect"
const stream = Stream.combine(
Stream.make("A", "B", "C"),
Stream.make(1, 2, 3),
() => true,
(takeLeft, pullLeft, pullRight) =>
takeLeft
? Effect.map(pullLeft, (value) => [`L:${value}`, false] as const)
: Effect.map(pullRight, (value) => [`R:${value}`, true] as const)
)
const program = Effect.gen(function*() {
const output = yield* Stream.runCollect(stream)
yield* Console.log(output)
})
Effect.runPromise(program)
// Output: [ "L:A", "R:1", "L:B", "R:2", "L:C", "R:3" ]merging
Source effect/Stream.ts:727739 lines
export const const combine: {
<A2, E2, R2, S, E, A, A3, E3, R3>(
that: Stream<A2, E2, R2>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
): <R>(
self: Stream<A, E, R>
) => Stream<A3, E3, R2 | R3 | R>
<A, E, R, A2, E2, R2, S, A3, E3, R3>(
self: Stream<A, E, R>,
that: Stream<A2, E2, R2>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
): Stream<A3, E3, R | R2 | R3>
}
Combines elements from this stream and the specified stream by repeatedly
applying a stateful function that can pull from either side.
Details
Where possible, prefer Stream.combineArray for a more efficient
implementation.
Example (Combining streams with state)
import { Console, Effect, Stream } from "effect"
const stream = Stream.combine(
Stream.make("A", "B", "C"),
Stream.make(1, 2, 3),
() => true,
(takeLeft, pullLeft, pullRight) =>
takeLeft
? Effect.map(pullLeft, (value) => [`L:${value}`, false] as const)
: Effect.map(pullRight, (value) => [`R:${value}`, true] as const)
)
const program = Effect.gen(function*() {
const output = yield* Stream.runCollect(stream)
yield* Console.log(output)
})
Effect.runPromise(program)
// Output: [ "L:A", "R:1", "L:B", "R:2", "L:C", "R:3" ]
combine: {
<function (type parameter) A2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A2, function (type parameter) E2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E2, function (type parameter) R2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R2, function (type parameter) S in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>S, function (type parameter) E in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E, function (type parameter) A in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A, function (type parameter) A3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A3, function (type parameter) E3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E3, function (type parameter) R3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R3>(
that: Stream<A2, E2, R2>(parameter) that: {
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) A2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A2, function (type parameter) E2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E2, function (type parameter) R2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R2>,
s: LazyArg<S>s: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) S in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
s: Ss: function (type parameter) S in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>S,
pullLeft: Pull.Pull<A, E, void>(parameter) pullLeft: {
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<function (type parameter) A in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A, function (type parameter) E in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E, void>,
pullRight: Pull.Pull<A2, E2, void>(parameter) pullRight: {
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<function (type parameter) A2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A2, function (type parameter) E2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E2, void>
) => 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<readonly [function (type parameter) A3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A3, function (type parameter) S in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>S], function (type parameter) E3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E3, function (type parameter) R3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R3>
): <function (type parameter) R in <R>(self: Stream<A, E, R>): Stream<A3, E3, R2 | R3 | 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 <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A, function (type parameter) E in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E, function (type parameter) R in <R>(self: Stream<A, E, R>): Stream<A3, E3, R2 | R3 | 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) A3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>A3, function (type parameter) E3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>E3, function (type parameter) R2 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R2 | function (type parameter) R3 in <A2, E2, R2, S, E, A, A3, E3, R3>(that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): <R>(self: Stream<A, E, R>) => Stream<A3, E3, R2 | R3 | R>R3 | function (type parameter) R in <R>(self: Stream<A, E, R>): Stream<A3, E3, R2 | R3 | R>R>
<function (type parameter) A in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R, function (type parameter) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2, function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S, function (type parameter) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3>(
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, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R>,
that: Stream<A2, E2, R2>(parameter) that: {
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) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2>,
s: LazyArg<S>s: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
s: Ss: function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S,
pullLeft: Pull.Pull<A, E, void>(parameter) pullLeft: {
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<function (type parameter) A in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, void>,
pullRight: Pull.Pull<A2, E2, void>(parameter) pullRight: {
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<function (type parameter) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, void>
) => 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<readonly [function (type parameter) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S], function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3>
): 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) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R | function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2 | function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3>
} = dual<(...args: Array<any>) => any, <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>) => Stream<A3, E3, R | R2 | R3>>(arity: 4, body: <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>) => Stream<A3, E3, R | R2 | R3>): ((...args: Array<any>) => any) & (<A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>) => Stream<A3, E3, R | R2 | R3>) (+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(4, <function (type parameter) A in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R, function (type parameter) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2, function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S, function (type parameter) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3>(
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, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R>,
that: Stream<A2, E2, R2>(parameter) that: {
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) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2>,
s: LazyArg<S>s: type LazyArg<A> = () => AA zero-argument function that produces a value when invoked.
When to use
Use to type a lazy value provider that should not run until called.
Example (Creating a lazy argument)
import { Function } from "effect"
const constNull: Function.LazyArg<null> = Function.constant(null)
LazyArg<function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S>,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
s: Ss: function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S,
pullLeft: Pull.Pull<A, E, void>(parameter) pullLeft: {
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<function (type parameter) A in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A, function (type parameter) E in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E, void>,
pullRight: Pull.Pull<A2, E2, void>(parameter) pullRight: {
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<function (type parameter) A2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E2, void>
) => 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<readonly [function (type parameter) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) S in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>S], function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3>
): 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) A3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>A3, function (type parameter) E3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>E3, function (type parameter) R in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R | function (type parameter) R2 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R2 | function (type parameter) R3 in <A, E, R, A2, E2, R2, S, A3, E3, R3>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>, s: LazyArg<S>, f: (s: S, pullLeft: Pull.Pull<A, E, void>, pullRight: Pull.Pull<A2, E2, void>) => Effect.Effect<readonly [A3, S], E3, R3>): Stream<A3, E3, R | R2 | R3>R3> =>
import ChannelChannel.const combine: {
<
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2,
S,
OutElem,
OutErr,
OutDone,
A,
E,
R
>(
that: Channel<
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2
>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<
OutElem,
OutErr,
OutDone
>,
pullRight: Pull.Pull<
OutElem2,
OutErr2,
OutDone2
>
) => Effect.Effect<readonly [A, S], E, R>
): <InElem, InErr, InDone, Env>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
A,
Pull.ExcludeDone<E>,
Cause.Done.Extract<E>,
InElem & InElem2,
InErr & InErr2,
InDone & InDone2,
Env | Env2 | R
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2,
S,
A,
E,
R
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
that: Channel<
OutElem2,
OutErr2,
OutDone2,
InElem2,
InErr2,
InDone2,
Env2
>,
s: LazyArg<S>,
f: (
s: S,
pullLeft: Pull.Pull<
OutElem,
OutErr,
OutDone
>,
pullRight: Pull.Pull<
OutElem2,
OutErr2,
OutDone2
>
) => Effect.Effect<readonly [A, S], E, R>
): Channel<
A,
Pull.ExcludeDone<E>,
Cause.Done.Extract<E>,
InElem & InElem2,
InErr & InErr2,
InDone & InDone2,
Env | Env2 | R
>
}
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; <…;
}
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(that: Stream<A2, E2, R2>(parameter) that: {
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<A2, E2, R2>.channel: Channel.Channel<Arr.NonEmptyReadonlyArray<A>, E, void, unknown, unknown, unknown, R>(property) Stream<A2, E2, R2>.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; <…;
}
s: LazyArg<S>s,
f: (
s: S,
pullLeft: Pull.Pull<A, E, void>,
pullRight: Pull.Pull<A2, E2, void>
) => Effect.Effect<readonly [A3, S], E3, R3>
Pipeable.pipe<Channel.Channel<A3, Exclude<E3, Cause.Done<any>>, Cause.Done<A = void>.Extract<E3>, unknown, unknown, unknown, R | R2 | R3>, Channel.Channel<[A3, ...A3[]], Exclude<E3, Cause.Done<any>>, Cause.Done.Extract<E3>, unknown, unknown, unknown, R | R2 | R3>, Stream<A3, Exclude<E3, Cause.Done<any>>, R | R2 | R3>>(this: Channel.Channel<...>, ab: (_: Channel.Channel<A3, Exclude<E3, Cause.Done<any>>, Cause.Done.Extract<E3>, unknown, unknown, unknown, R | ... 1 more ... | R3>) => Channel.Channel<...>, bc: (_: Channel.Channel<...>) => Stream<...>): Stream<...> (+21 overloads)pipe(
import ChannelChannel.const map: {
<OutElem, OutElem2>(
f: (o: OutElem, i: number) => OutElem2
): <
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem2,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
OutElem2
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
f: (o: OutElem, i: number) => OutElem2
): Channel<
OutElem2,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
}
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 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
))