<A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(
self: Result<A, E>
) => Result<A2, E | E2>
<A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<
A2,
E | E2
>Chains a function that returns a Result onto a successful value.
When to use
Use to sequence Result-returning computations that should short-circuit on
failure.
Details
- If
selfis aSuccess, appliesfto the value and returns the resultingResult - If
selfis aFailure, short-circuits and returns it unchanged - The error types are merged into a union (
E | E2) - This is the monadic
bind/>>=forResult
Example (Validating sequentially)
import { pipe, Result } from "effect"
const result = pipe(
Result.succeed(5),
Result.flatMap((n) =>
n > 0 ? Result.succeed(n * 2) : Result.fail("not positive")
)
)
console.log(result)
// Output: { _tag: "Success", success: 10, ... }export const const flatMap: {
<A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(
self: Result<A, E>
) => Result<A2, E | E2>
<A, E, A2, E2>(
self: Result<A, E>,
f: (a: A) => Result<A2, E2>
): Result<A2, E | E2>
}
Chains a function that returns a Result onto a successful value.
When to use
Use to sequence Result-returning computations that should short-circuit on
failure.
Details
- If
self is a Success, applies f to the value and returns the resulting Result
- If
self is a Failure, short-circuits and returns it unchanged
- The error types are merged into a union (
E | E2)
- This is the monadic
bind / >>= for Result
Example (Validating sequentially)
import { pipe, Result } from "effect"
const result = pipe(
Result.succeed(5),
Result.flatMap((n) =>
n > 0 ? Result.succeed(n * 2) : Result.fail("not positive")
)
)
console.log(result)
// Output: { _tag: "Success", success: 10, ... }
flatMap: {
<function (type parameter) A in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>A, function (type parameter) A2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>A2, function (type parameter) E2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>E2>(f: (a: A) => Result<A2, E2>f: (a: Aa: function (type parameter) A in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>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<function (type parameter) A2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>A2, function (type parameter) E2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>E2>): <function (type parameter) E in <E>(self: Result<A, E>): Result<A2, E | E2>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, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>A, function (type parameter) E in <E>(self: Result<A, E>): Result<A2, E | E2>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<function (type parameter) A2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>A2, function (type parameter) E in <E>(self: Result<A, E>): Result<A2, E | E2>E | function (type parameter) E2 in <A, A2, E2>(f: (a: A) => Result<A2, E2>): <E>(self: Result<A, E>) => Result<A2, E | E2>E2>
<function (type parameter) A in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E, function (type parameter) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2>(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, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E>, f: (a: A) => Result<A2, E2>f: (a: Aa: function (type parameter) A in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>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<function (type parameter) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2>): 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) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E | function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2>
} = import dualdual(
2,
<function (type parameter) A in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E, function (type parameter) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2>(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, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E>, f: (a: A) => Result<A2, E2>f: (a: Aa: function (type parameter) A in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>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<function (type parameter) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2>): 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) A2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>A2, function (type parameter) E in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E | function (type parameter) E2 in <A, E, A2, E2>(self: Result<A, E>, f: (a: A) => Result<A2, E2>): Result<A2, E | E2>E2> =>
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) ? 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(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) : f: (a: A) => Result<A2, E2>f(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)
)