<A, B, C>(f: (a: A) => Result<C, B>): (
self: Option<A>
) => [left: Option<B>, right: Option<C>]
<A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [
left: Option<B>,
right: Option<C>
]Splits an Option into two Options using a function that returns a Result.
When to use
Use when you need to split an optional value into "left" and "right"
channels using a Result-returning function.
Details
None→[None, None]SomewherefreturnsErr→[Some(error), None]SomewherefreturnsOk→[None, Some(value)]
Example (Partitioning by Result)
import { Option, Result } from "effect"
const parseNumber = (s: string): Result.Result<number, string> => {
const n = Number(s)
return isNaN(n) ? Result.fail("Not a number") : Result.succeed(n)
}
console.log(Option.partitionMap(Option.some("42"), parseNumber))
// Output: [{ _id: 'Option', _tag: 'None' }, { _id: 'Option', _tag: 'Some', value: 42 }]
console.log(Option.partitionMap(Option.some("abc"), parseNumber))
// Output: [{ _id: 'Option', _tag: 'Some', value: 'Not a number' }, { _id: 'Option', _tag: 'None' }]
console.log(Option.partitionMap(Option.none(), parseNumber))
// Output: [{ _id: 'Option', _tag: 'None' }, { _id: 'Option', _tag: 'None' }]export const const partitionMap: {
<A, B, C>(f: (a: A) => Result<C, B>): (
self: Option<A>
) => [left: Option<B>, right: Option<C>]
<A, B, C>(
self: Option<A>,
f: (a: A) => Result<C, B>
): [left: Option<B>, right: Option<C>]
}
Splits an Option into two Options using a function that returns a Result.
When to use
Use when you need to split an optional value into "left" and "right"
channels using a Result-returning function.
Details
None → [None, None]Some where f returns Err → [Some(error), None]Some where f returns Ok → [None, Some(value)]
Example (Partitioning by Result)
import { Option, Result } from "effect"
const parseNumber = (s: string): Result.Result<number, string> => {
const n = Number(s)
return isNaN(n) ? Result.fail("Not a number") : Result.succeed(n)
}
console.log(Option.partitionMap(Option.some("42"), parseNumber))
// Output: [{ _id: 'Option', _tag: 'None' }, { _id: 'Option', _tag: 'Some', value: 42 }]
console.log(Option.partitionMap(Option.some("abc"), parseNumber))
// Output: [{ _id: 'Option', _tag: 'Some', value: 'Not a number' }, { _id: 'Option', _tag: 'None' }]
console.log(Option.partitionMap(Option.none(), parseNumber))
// Output: [{ _id: 'Option', _tag: 'None' }, { _id: 'Option', _tag: 'None' }]
partitionMap: {
<function (type parameter) A in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]A, function (type parameter) B in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]B, function (type parameter) C in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]C>(f: (a: A) => Result<C, B>f: (a: Aa: function (type parameter) A in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]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) C in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]C, function (type parameter) B in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]B>): (self: Option<A>self: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]A>) => [Option<B>left: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) B in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]B>, Option<C>right: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) C in <A, B, C>(f: (a: A) => Result<C, B>): (self: Option<A>) => [left: Option<B>, right: Option<C>]C>]
<function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]A, function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]B, function (type parameter) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]C>(self: Option<A>self: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]A>, f: (a: A) => Result<C, B>f: (a: Aa: function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]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) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]C, function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]B>): [Option<B>left: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]B>, Option<C>right: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [left: Option<B>, right: Option<C>]C>]
} = import dualdual(2, <function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]A, function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]B, function (type parameter) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]C>(
self: Option<A>self: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]A>,
f: (a: A) => Result<C, B>f: (a: Aa: function (type parameter) A in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]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) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]C, function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]B>
): [Option<B>excluded: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) B in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]B>, Option<C>satisfying: type Option<A> = None<A> | Some<A>The Option data type represents optional values. An Option<A> is either
Some<A>, containing a value of type A, or None, representing absence.
When to use
Use to represent initial values that may not yet exist
- Returning from partial functions (not defined for all inputs)
- Managing optional fields in data structures
Namespace containing utility types for Option.
When to use
Use to access type-level helpers associated with Option.
Option<function (type parameter) C in <A, B, C>(self: Option<A>, f: (a: A) => Result<C, B>): [excluded: Option<B>, satisfying: Option<C>]C>] => {
if (const isNone: <A>(
self: Option<A>
) => self is None<A>
Checks whether an Option is None (absent).
When to use
Use when you need to branch on an absent Option before accessing .value.
Details
- Acts as a type guard, narrowing to
None<A>
Example (Checking for None)
import { Option } from "effect"
console.log(Option.isNone(Option.some(1)))
// Output: false
console.log(Option.isNone(Option.none()))
// Output: true
isNone(self: Option<A>self)) {
return [const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none(), const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none()]
}
const const e: Result<C, B>e = f: (a: A) => Result<C, B>f(self: Option<A>(parameter) self: {
_tag: "Some";
_op: "Some";
value: A;
valueOrUndefined: 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;
}
Some<A>.value: Avalue)
return import resultresult.const isFailure: <A, E>(
result: Result.Result<A, E>
) => result is Result.Failure<A, E>
const e: Result<C, B>e) ? [const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some(const e: Failure<C, B>const e: {
_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<C, B>.failure: Bfailure), const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none()] : [const none: <A = never>() => Option<A>Creates an Option representing the absence of a value.
When to use
Use to represent a missing or uninitialized value, such as returning "no
result" from a function.
Details
- Returns
Option<never>, which is a subtype of Option<A> for any A
- Always returns the same singleton instance
Example (Creating an empty Option)
import { Option } from "effect"
// ┌─── Option<never>
// ▼
const noValue = Option.none()
console.log(noValue)
// Output: { _id: 'Option', _tag: 'None' }
none(), const some: <A>(value: A) => Option<A>Wraps the given value into an Option to represent its presence.
When to use
Use to wrap a known present value as Option
- Returning a successful result from a partial function
Details
- Always returns
Some<A>
- Does not filter
null or undefined; use
fromNullishOr
for that
Example (Wrapping a value)
import { Option } from "effect"
// ┌─── Option<number>
// ▼
const value = Option.some(1)
console.log(value)
// Output: { _id: 'Option', _tag: 'Some', value: 1 }
some(const e: Success<C, B>const e: {
_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<C, B>.success: Csuccess)]
})