<E, A2, E2, R2>(
f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>
): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>
): Stream<A, E | E2, R | R2>Runs an effect when the stream fails without changing its values or error, unless the tap effect itself fails.
Example (Tapping stream causes)
import { Cause, Console, Effect, Stream } from "effect"
const stream = Stream.make(1, 2).pipe(
Stream.concat(Stream.fail("boom")),
Stream.tapCause((cause) => Console.log(Cause.isReason(cause))),
Stream.catch(() => Stream.succeed(0))
)
const program = Effect.gen(function* () {
const result = yield* Stream.runCollect(stream)
yield* Console.log(result)
})
Effect.runPromise(program)
// Output: true
// Output: [ 1, 2, 0 ]export const const tapCause: {
<E, A2, E2, R2>(
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, R2>
): <A, R>(
self: Stream<A, E, R>
) => Stream<A, E | E2, R2 | R>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, R2>
): Stream<A, E | E2, R | R2>
}
Runs an effect when the stream fails without changing its values or error,
unless the tap effect itself fails.
Example (Tapping stream causes)
import { Cause, Console, Effect, Stream } from "effect"
const stream = Stream.make(1, 2).pipe(
Stream.concat(Stream.fail("boom")),
Stream.tapCause((cause) => Console.log(Cause.isReason(cause))),
Stream.catch(() => Stream.succeed(0))
)
const program = Effect.gen(function* () {
const result = yield* Stream.runCollect(stream)
yield* Console.log(result)
})
Effect.runPromise(program)
// Output: true
// Output: [ 1, 2, 0 ]
tapCause: {
<function (type parameter) E in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E, function (type parameter) A2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>A2, function (type parameter) E2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2>(
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, R2>
cause: Cause.Cause<E>(parameter) cause: {
reasons: ReadonlyArray<Reason<E>>;
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 CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E>) => import EffectEffect.interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>A2, function (type parameter) E2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2>
): <function (type parameter) A in <A, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) R in <A, 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, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) E in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E, function (type parameter) R in <A, 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, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>A, function (type parameter) E in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E | function (type parameter) E2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>E2, function (type parameter) R2 in <E, A2, E2, R2>(f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): <A, R>(self: Stream<A, E, R>) => Stream<A, E | E2, R2 | R>R2 | function (type parameter) R in <A, R>(self: Stream<A, E, R>): Stream<A, E | E2, R2 | R>R>
<function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R>,
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, R2>
cause: Cause.Cause<E>(parameter) cause: {
reasons: ReadonlyArray<Reason<E>>;
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 CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E>) => import EffectEffect.interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R2>
} = dual<(...args: Array<any>) => any, <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>) => Stream<A, E | E2, R | R2>>(arity: 2, body: <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>) => Stream<A, E | E2, R | R2>): ((...args: Array<any>) => any) & (<A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R>,
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, R2>
cause: Cause.Cause<E>(parameter) cause: {
reasons: ReadonlyArray<Reason<E>>;
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 CauseCause.interface Cause<out E>A structured representation of how an Effect failed.
When to use
Use to preserve the full structured failure information for an effect instead
of collapsing it to a single error value.
Details
Access the individual failure entries through the reasons array, then
narrow each entry with
isFailReason
,
isDieReason
, or
- Use
hasFails
/
hasDies
/
hasInterrupts
to test
for the presence of specific reason kinds without iterating.
- Use
findError
/
findDefect
to extract the first value
of a given kind.
- Use
combine
to merge two causes.
Cause implements Equal — two causes with the same reasons (by value)
compare as equal.
Example (Creating and inspecting a cause)
import { Cause } from "effect"
const cause = Cause.fail("Something went wrong")
console.log(cause.reasons.length) // 1
console.log(Cause.isFailReason(cause.reasons[0])) // true
Companion namespace for the Cause interface.
Cause<function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E>) => import EffectEffect.interface Effect<out A, out E = never, out R = never>The Effect interface defines a value that lazily describes a workflow or
job. The workflow requires some context R, and may fail with an error of
type E, or succeed with a value of type A.
When to use
Use when you need to represent a lazy, composable workflow that can require
services, fail with a typed error, or succeed with a typed value.
Details
Effect values model resourceful interaction with the outside world,
including synchronous, asynchronous, concurrent, and parallel interaction.
They use a fiber-based concurrency model, with built-in support for
scheduling, fine-grained interruption, structured concurrency, and high
scalability.
To run an Effect value, you need a Runtime, which is a type that is
capable of executing Effect values.
Effect<function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, E2, R2>): Stream<A, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, f: (cause: Cause.Cause<E>) => Effect.Effect<A2, 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; <…;
}
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; <…;
}
Pipeable.pipe<Channel.Channel<readonly [A, ...A[]], E, void, unknown, unknown, unknown, R>, Channel.Channel<readonly [A, ...A[]], E | E2, void, unknown, unknown, unknown, R | R2>, Stream<A, E | E2, R | R2>>(this: Channel.Channel<...>, ab: (_: Channel.Channel<readonly [A, ...A[]], E, void, unknown, unknown, unknown, R>) => Channel.Channel<readonly [A, ...A[]], E | E2, void, unknown, unknown, unknown, R | R2>, bc: (_: Channel.Channel<readonly [A, ...A[]], E | E2, void, unknown, unknown, unknown, R | R2>) => Stream<A, E | E2, R | R2>): Stream<...> (+21 overloads)pipe(
import ChannelChannel.const tapCause: {
<OutErr, A, E, R>(
f: (
d: Cause.Cause<OutErr>
) => Effect.Effect<A, E, R>
): <
OutElem,
OutDone,
InElem,
InErr,
InDone,
Env
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>
) => Channel<
OutElem,
OutErr | E,
OutDone | void,
InElem,
InErr,
InDone,
Env | R
>
<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env,
A,
E,
R
>(
self: Channel<
OutElem,
OutErr,
OutDone,
InElem,
InErr,
InDone,
Env
>,
f: (
d: Cause.Cause<OutErr>
) => Effect.Effect<A, E, R>
): Channel<
OutElem,
OutErr | E,
OutDone | void,
InElem,
InErr,
InDone,
Env | R
>
}
f: (
cause: Cause.Cause<E>
) => Effect.Effect<A2, E2, 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
))