<A, E>(self: Result<A, E>): self is Success<A, E>Checks whether a Result is a Success.
When to use
Use to narrow a known Result to the Success variant.
Details
- Acts as a TypeScript type guard, narrowing to
Success<A, E> - After narrowing, you can access
.successto read the value
Example (Narrowing to success)
import { Result } from "effect"
const result = Result.succeed(42)
if (Result.isSuccess(result)) {
console.log(result.success)
// Output: 42
}export const const isSuccess: <A, E>(
self: Result<A, E>
) => self is Success<A, E>
Checks whether a Result is a Success.
When to use
Use to narrow a known Result to the Success variant.
Details
- Acts as a TypeScript type guard, narrowing to
Success<A, E>
- After narrowing, you can access
.success to read the value
Example (Narrowing to success)
import { Result } from "effect"
const result = Result.succeed(42)
if (Result.isSuccess(result)) {
console.log(result.success)
// Output: 42
}
isSuccess: <function (type parameter) A in <A, E>(self: Result<A, E>): self is Success<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Success<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 Success<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Success<A, E>E>) => self: Result<A, E>self is interface Success<out A, out E>The success variant of
Result
. Wraps a value of type A.
Details
- Access the value via the
.success property
- Use
isSuccess
to narrow a
Result to Success
- Create with
succeed
Example (Accessing the success value)
import { Result } from "effect"
const success = Result.succeed(42)
if (Result.isSuccess(success)) {
console.log(success.success)
// Output: 42
}
Success<function (type parameter) A in <A, E>(self: Result<A, E>): self is Success<A, E>A, function (type parameter) E in <A, E>(self: Result<A, E>): self is Success<A, E>E> = import resultresult.const isSuccess: <A, E>(
result: Result.Result<A, E>
) => result is Result.Success<A, E>