<A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>Lifts failures and successes into a Result, yielding a stream that cannot fail.
Details
The stream ends after the first failure, emitting a Result.fail value.
Example (Converting failures to results)
import { Console, Effect, Result, Stream } from "effect"
const program = Effect.gen(function*() {
const results = yield* Stream.make(1, 2).pipe(
Stream.concat(Stream.fail("boom")),
Stream.result,
Stream.map(Result.match({
onFailure: (error) => `failure: ${error}`,
onSuccess: (value) => `success: ${value}`
})),
Stream.runCollect
)
yield* Console.log(results)
})
Effect.runPromise(program)
// Output: [ "success: 1", "success: 2", "failure: boom" ]export const const result: <A, E, R>(
self: Stream<A, E, R>
) => Stream<Result.Result<A, E>, never, R>
Lifts failures and successes into a Result, yielding a stream that cannot fail.
Details
The stream ends after the first failure, emitting a Result.fail value.
Example (Converting failures to results)
import { Console, Effect, Result, Stream } from "effect"
const program = Effect.gen(function*() {
const results = yield* Stream.make(1, 2).pipe(
Stream.concat(Stream.fail("boom")),
Stream.result,
Stream.map(Result.match({
onFailure: (error) => `failure: ${error}`,
onSuccess: (value) => `success: ${value}`
})),
Stream.runCollect
)
yield* Console.log(results)
})
Effect.runPromise(program)
// Output: [ "success: 1", "success: 2", "failure: boom" ]
result = <function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, 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<Result.Result<A, E>, never, R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, 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<import ResultResult.type Result<A, E = never> = Result.Success<A, E> | Result.Failure<A, E>A value that is either Success<A, E> or Failure<A, E>.
When to use
Use when both success and failure should remain available as data and
Option would lose failure information.
Details
- Use
succeed
/
fail
to construct
- Use
match
to fold both branches
- Use
isSuccess
/
isFailure
to narrow the type
E defaults to never, so Result<number> means a result that cannot fail.
Example (Creating and matching a Result)
import { Result } from "effect"
const success = Result.succeed(42)
const failure = Result.fail("something went wrong")
const message = Result.match(success, {
onSuccess: (value) => `Success: ${value}`,
onFailure: (error) => `Error: ${error}`
})
console.log(message)
// Output: "Success: 42"
Namespace containing type-level utilities for extracting the inner types
of a Result.
Example (Extracting inner types)
import type { Result } from "effect"
type R = Result.Result<number, string>
// number
type A = Result.Result.Success<R>
// string
type E = Result.Result.Failure<R>
Result<function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, R>E>, never, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, E>, never, 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; <…;
}
Pipeable.pipe<Stream<A, E, R>, Stream<Result.Result<A, never>, E, R>, Stream<Result.Result<A, never> | Result.Result<never, E>, never, R>>(this: Stream<A, E, R>, ab: (_: Stream<A, E, R>) => Stream<Result.Result<A, never>, E, R>, bc: (_: Stream<Result.Result<A, never>, E, R>) => Stream<Result.Result<A, never> | Result.Result<never, E>, never, R>): Stream<...> (+21 overloads)pipe(
const map: {
<A, B>(f: (a: A, i: number) => B): <E, R>(
self: Stream<A, E, R>
) => Stream<B, E, R>
<A, E, R, B>(
self: Stream<A, E, R>,
f: (a: A, i: number) => B
): Stream<B, E, R>
}
import ResultResult.const succeed: <A>(right: A) => Result<A>Creates a Result holding a Success value.
Details
- Use when you have a value and want to lift it into the
Result type
- The error type
E defaults to never
Example (Wrapping a value)
import { Result } from "effect"
const result = Result.succeed(42)
console.log(Result.isSuccess(result))
// Output: true
succeed),
const catch_: {
<E, A2, E2, R2>(
f: (error: E) => Stream<A2, E2, R2>
): <A, R>(
self: Stream<A, E, R>
) => Stream<A | A2, E2, R2 | R>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
f: (error: E) => Stream<A2, E2, R2>
): Stream<A | A2, E2, R | R2>
}
e: Ee) => const succeed: <A>(value: A) => Stream<A>Creates a single-valued pure stream.
Example (Creating a single-valued pure stream)
import { Console, Effect, Stream } from "effect"
const program = Effect.gen(function*() {
const values = yield* Stream.succeed(3).pipe(Stream.runCollect)
yield* Console.log(values)
})
Effect.runPromise(program)
// [ 3 ]
succeed(import ResultResult.const fail: <E>(
left: E
) => Result<never, E>
Creates a Result holding a Failure value.
When to use
Use to represent a failed Result with a typed failure value.
Details
- The success type
A defaults to never
Example (Creating a failure)
import { Result } from "effect"
const result = Result.fail("Something went wrong")
console.log(Result.isFailure(result))
// Output: true
fail(e: Ee)))
)