<E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | A
<A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2Extracts the success value, or computes a fallback from the error.
When to use
Use when you need the success value from a Result, with a fallback computed
from the failure value.
Details
Success<A>returns the inner valueFailure<E>appliesonFailureto the error and returns the result- The return type is
A | A2(union of both branches)
Example (Providing a fallback)
import { Result } from "effect"
console.log(Result.getOrElse(Result.succeed(1), () => 0))
// Output: 1
console.log(Result.getOrElse(Result.fail("err"), () => 0))
// Output: 0export const const getOrElse: {
<E, A2>(onFailure: (err: E) => A2): <A>(
self: Result<A, E>
) => A2 | A
<A, E, A2>(
self: Result<A, E>,
onFailure: (err: E) => A2
): A | A2
}
Extracts the success value, or computes a fallback from the error.
When to use
Use when you need the success value from a Result, with a fallback computed
from the failure value.
Details
Success<A> returns the inner valueFailure<E> applies onFailure to the error and returns the result- The return type is
A | A2 (union of both branches)
Example (Providing a fallback)
import { Result } from "effect"
console.log(Result.getOrElse(Result.succeed(1), () => 0))
// Output: 1
console.log(Result.getOrElse(Result.fail("err"), () => 0))
// Output: 0
getOrElse: {
<function (type parameter) E in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AE, function (type parameter) A2 in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AA2>(onFailure: (err: E) => A2onFailure: (err: Eerr: function (type parameter) E in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AE) => function (type parameter) A2 in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AA2): <function (type parameter) A in <A>(self: Result<A, E>): A2 | AA>(self: Result<A, E>self: 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>(self: Result<A, E>): A2 | AA, function (type parameter) E in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AE>) => function (type parameter) A2 in <E, A2>(onFailure: (err: E) => A2): <A>(self: Result<A, E>) => A2 | AA2 | function (type parameter) A in <A>(self: Result<A, E>): A2 | AA
<function (type parameter) A in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A, function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E, function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2>(self: Result<A, E>self: 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, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A, function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E>, onFailure: (err: E) => A2onFailure: (err: Eerr: function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E) => function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2): function (type parameter) A in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A | function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2
} = import dualdual(
2,
<function (type parameter) A in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A, function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E, function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2>(self: Result<A, E>self: 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, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A, function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E>, onFailure: (err: E) => A2onFailure: (err: Eerr: function (type parameter) E in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2E) => function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2): function (type parameter) A in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A | function (type parameter) A2 in <A, E, A2>(self: Result<A, E>, onFailure: (err: E) => A2): A | A2A2 =>
const isFailure: <A, E>(
self: Result<A, E>
) => self is Failure<A, E>
Checks whether a Result is a Failure.
When to use
Use to narrow a known Result to the Failure variant.
Details
- Acts as a TypeScript type guard, narrowing to
Failure<A, E>
- After narrowing, you can access
.failure to read the error value
Example (Narrowing to failure)
import { Result } from "effect"
const result = Result.fail("oops")
if (Result.isFailure(result)) {
console.log(result.failure)
// Output: "oops"
}
isFailure(self: Result<A, E>self) ? onFailure: (err: E) => A2onFailure(self: Result<A, E>(parameter) self: {
_tag: "Failure";
_op: "Failure";
failure: 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;
}
Failure<A, E>.failure: Efailure) : self: Result<A, E>(parameter) self: {
_tag: "Success";
_op: "Success";
success: 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;
}
Success<A, E>.success: Asuccess
)