<A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(
self: Stream<A, E, R>
) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
that: Stream<A2, E2, R2>
): Stream<Result.Result<A, A2>, E | E2, R | R2>Merges this stream and the specified stream together, tagging values from the
left stream as Result.succeed and values from the right stream as Result.fail.
When to use
Use when values from both streams should be emitted and downstream code needs
left values wrapped as successful Result values and right values wrapped as
failed Result values.
Example (Merging streams into results)
import { Console, Effect, Result, Stream } from "effect"
const left = Stream.fromEffect(Effect.succeed("left"))
const right = Stream.fromEffect(Effect.delay(Effect.succeed("right"), "10 millis"))
const merged = left.pipe(
Stream.mergeResult(right),
Stream.map(
Result.match({
onFailure: (value) => `right:${value}`,
onSuccess: (value) => `left:${value}`
})
)
)
const program = Effect.gen(function*() {
const result = yield* Stream.runCollect(merged)
yield* Console.log(result)
})
Effect.runPromise(program)
// Output: [ "left:left", "right:right" ]export const const mergeResult: {
<A2, E2, R2>(that: Stream<A2, E2, R2>): <
A,
E,
R
>(
self: Stream<A, E, R>
) => Stream<
Result.Result<A, A2>,
E2 | E,
R2 | R
>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
that: Stream<A2, E2, R2>
): Stream<Result.Result<A, A2>, E | E2, R | R2>
}
Merges this stream and the specified stream together, tagging values from the
left stream as Result.succeed and values from the right stream as Result.fail.
When to use
Use when values from both streams should be emitted and downstream code needs
left values wrapped as successful Result values and right values wrapped as
failed Result values.
Example (Merging streams into results)
import { Console, Effect, Result, Stream } from "effect"
const left = Stream.fromEffect(Effect.succeed("left"))
const right = Stream.fromEffect(Effect.delay(Effect.succeed("right"), "10 millis"))
const merged = left.pipe(
Stream.mergeResult(right),
Stream.map(
Result.match({
onFailure: (value) => `right:${value}`,
onSuccess: (value) => `left:${value}`
})
)
)
const program = Effect.gen(function*() {
const result = yield* Stream.runCollect(merged)
yield* Console.log(result)
})
Effect.runPromise(program)
// Output: [ "left:left", "right:right" ]
mergeResult: {
<function (type parameter) A2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>A2, function (type parameter) E2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>E2, function (type parameter) R2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>R2>(
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>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>A2, function (type parameter) E2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>E2, function (type parameter) R2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>R2>
): <function (type parameter) A in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, 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<Result.Result<A, A2>, E2 | E, R2 | R>A, function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, R2 | R>E, function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, 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<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, A2>, E2 | E, R2 | R>A, function (type parameter) A2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>A2>, function (type parameter) E2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>E2 | function (type parameter) E in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, R2 | R>E, function (type parameter) R2 in <A2, E2, R2>(that: Stream<A2, E2, R2>): <A, E, R>(self: Stream<A, E, R>) => Stream<Result.Result<A, A2>, E2 | E, R2 | R>R2 | function (type parameter) R in <A, E, R>(self: Stream<A, E, R>): Stream<Result.Result<A, A2>, E2 | E, R2 | R>R>
<function (type parameter) A in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, 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>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>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>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, 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<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, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2>, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R2>
} = dual<(...args: Array<any>) => any, <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>) => Stream<Result.Result<A, A2>, E | E2, R | R2>>(arity: 2, body: <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>) => Stream<Result.Result<A, A2>, E | E2, R | R2>): ((...args: Array<any>) => any) & (<A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>) => Stream<Result.Result<A, A2>, 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>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, 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>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>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>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2, function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, 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<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, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A, function (type parameter) A2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>A2>, function (type parameter) E in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E | function (type parameter) E2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>E2, function (type parameter) R in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R | function (type parameter) R2 in <A, E, R, A2, E2, R2>(self: Stream<A, E, R>, that: Stream<A2, E2, R2>): Stream<Result.Result<A, A2>, E | E2, R | R2>R2> =>
const merge: {
<A2, E2, R2>(
that: Stream<A2, E2, R2>,
options?:
| {
readonly haltStrategy?:
| HaltStrategy
| undefined
}
| undefined
): <A, E, R>(
self: Stream<A, E, R>
) => Stream<A | A2, E | E2, R | R2>
<A, E, R, A2, E2, R2>(
self: Stream<A, E, R>,
that: Stream<A2, E2, R2>,
options?:
| {
readonly haltStrategy?:
| HaltStrategy
| undefined
}
| undefined
): Stream<A | A2, E | E2, R | R2>
}
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>
}
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; <…;
}
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 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>
}
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; <…;
}
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)
)
)