<A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>Transforms Option<Result<A, E>> into Result<Option<A>, E>.
When to use
Use when optional absence should be treated as a successful None, while an
inner Result failure should still fail the whole result.
Details
NonebecomesSuccess(None)Some(Success(a))becomesSuccess(Some(a))Some(Failure(e))becomesFailure(e)
Example (Transposing an Option of a Result)
import { Option, Result } from "effect"
const some = Option.some(Result.succeed(42))
console.log(Result.transposeOption(some))
// Output: { _tag: "Success", success: { _tag: "Some", value: 42 }, ... }
const none = Option.none<Result.Result<number, string>>()
console.log(Result.transposeOption(none))
// Output: { _tag: "Success", success: { _tag: "None" }, ... }export const const transposeOption: <
A = never,
E = never
>(
self: Option<Result<A, E>>
) => Result<Option<A>, E>
Transforms Option<Result<A, E>> into Result<Option<A>, E>.
When to use
Use when optional absence should be treated as a successful None, while an
inner Result failure should still fail the whole result.
Details
None becomes Success(None)Some(Success(a)) becomes Success(Some(a))Some(Failure(e)) becomes Failure(e)
Example (Transposing an Option of a Result)
import { Option, Result } from "effect"
const some = Option.some(Result.succeed(42))
console.log(Result.transposeOption(some))
// Output: { _tag: "Success", success: { _tag: "Some", value: 42 }, ... }
const none = Option.none<Result.Result<number, string>>()
console.log(Result.transposeOption(none))
// Output: { _tag: "Success", success: { _tag: "None" }, ... }
transposeOption = <function (type parameter) A in <A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>A = never, function (type parameter) E in <A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>E = never>(
self: Option<Result<A, E>>self: import OptionOption<type Result<A, E = never> = Success<A, E> | 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 = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>A, function (type parameter) E in <A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>E>>
): type Result<A, E = never> = Success<A, E> | 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<import OptionOption<function (type parameter) A in <A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>A>, function (type parameter) E in <A = never, E = never>(self: Option<Result<A, E>>): Result<Option<A>, E>E> => {
return import option_option_.const isNone: <A>(
fa: Option.Option<A>
) => fa is Option.None<A>
self: Option<Result<A, E>>self) ? const succeedNone: Result<
Option<never>,
never
>
Provides a pre-built Result<Option<never>> that succeeds with None.
When to use
Use when an optional success should be absent, such as the None branch of
transposeOption or transposeMapOption.
Details
This is equivalent to Result.succeed(Option.none()), but reuses a shared
Success wrapper instead of allocating one each time.
Example (Succeeding with None)
import { Result } from "effect"
console.log(Result.isSuccess(Result.succeedNone))
// Output: true
succeedNone : const map: {
<A, A2>(f: (ok: A) => A2): <E>(
self: Result<A, E>
) => Result<A2, E>
<A, E, A2>(
self: Result<A, E>,
f: (ok: A) => A2
): Result<A2, E>
}
self: Option<Result<A, E>>(parameter) self: {
_tag: "Some";
_op: "Some";
value: A;
valueOrUndefined: A;
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 option_option_.const some: <A>(
value: A
) => Option.Option<A>