<A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>
<A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>Converts a possibly null or undefined value into a Result.
When to use
Use when you need null or undefined input to become a Failure while
present values remain available as Success.
Details
- Non-nullish values become
Success<NonNullable<A>> nullorundefinedbecomesFailure<E>using the provided function- Supports both data-first and data-last (piped) usage
- The
onNullishcallback receives the original value
Example (Handling nullable values)
import { Result } from "effect"
console.log(Result.fromNullishOr(1, () => "fallback"))
// Output: { _tag: "Success", success: 1, ... }
console.log(Result.fromNullishOr(null, () => "fallback"))
// Output: { _tag: "Failure", failure: "fallback", ... }export const const fromNullishOr: {
<A, E>(onNullish: (a: A) => E): (
self: A
) => Result<NonNullable<A>, E>
<A, E>(self: A, onNullish: (a: A) => E): Result<
NonNullable<A>,
E
>
}
Converts a possibly null or undefined value into a Result.
When to use
Use when you need null or undefined input to become a Failure while
present values remain available as Success.
Details
- Non-nullish values become
Success<NonNullable<A>>
null or undefined becomes Failure<E> using the provided function- Supports both data-first and data-last (piped) usage
- The
onNullish callback receives the original value
Example (Handling nullable values)
import { Result } from "effect"
console.log(Result.fromNullishOr(1, () => "fallback"))
// Output: { _tag: "Success", success: 1, ... }
console.log(Result.fromNullishOr(null, () => "fallback"))
// Output: { _tag: "Failure", failure: "fallback", ... }
fromNullishOr: {
<function (type parameter) A in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>A, function (type parameter) E in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>E>(onNullish: (a: A) => EonNullish: (a: Aa: function (type parameter) A in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>A) => function (type parameter) E in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>E): (self: Aself: function (type parameter) A in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>A) => 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<type NonNullable<T> = T & {}Exclude null and undefined from T
NonNullable<function (type parameter) A in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>A>, function (type parameter) E in <A, E>(onNullish: (a: A) => E): (self: A) => Result<NonNullable<A>, E>E>
<function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A, function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>E>(self: Aself: function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A, onNullish: (a: A) => EonNullish: (a: Aa: function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A) => function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<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<type NonNullable<T> = T & {}Exclude null and undefined from T
NonNullable<function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A>, function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>E>
} = import dualdual(
2,
<function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A, function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>E>(self: Aself: function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A, onNullish: (a: A) => EonNullish: (a: Aa: function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A) => function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<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<type NonNullable<T> = T & {}Exclude null and undefined from T
NonNullable<function (type parameter) A in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>A>, function (type parameter) E in <A, E>(self: A, onNullish: (a: A) => E): Result<NonNullable<A>, E>E> =>
self: Aself == null ? 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(onNullish: (a: A) => EonNullish(self: Aself)) : 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(self: NonNullable<A>self)
)