<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
.failureto 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"
}export const 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: <function (type parameter) A in <A, E>(self: Result<A, E>): self is Failure<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Failure<A, E>E>(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>(self: Result<A, E>): self is Failure<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Failure<A, E>E>) => self: Result<A, E>self is interface Failure<out A, out E>The failure variant of
Result
. Wraps an error of type E.
Details
- Access the error via the
.failure property
- Use
isFailure
to narrow a
Result to Failure
- Create with
fail
Example (Accessing the failure value)
import { Result } from "effect"
const failure = Result.fail("Network error")
if (Result.isFailure(failure)) {
console.log(failure.failure)
// Output: "Network error"
}
Failure<function (type parameter) A in <A, E>(self: Result<A, E>): self is Failure<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Failure<A, E>E> = import resultresult.const isFailure: <A, E>(
result: Result.Result<A, E>
) => result is Result.Failure<A, E>