Interface Option<T>

An Option jonad.

Represents a value that may or may not be present. The left-side value is Some, while the right-side value is None (represented by the value null).

interface Option<T> {
 andThen(mapper: Mapper<T, Option>): Option;
 andThenAsync(mapper: AsyncMapper<T, Option>): Promise<Option>;
 getLeftOrThrow(): T;
 getRightOrThrow(): null;
 isLeft(): boolean;
 isNone(): boolean;
 isRight(): boolean;
 isSome(): boolean;
 leftOr(fallback: T | Mapper<null, T>): T;
 leftOrAsync(fallback: T | Promise<T> | AsyncMapper<null, T>): Promise<T>;
 map(mapper: Mapper<T, U>): Option;
 mapAsync(mapper: AsyncMapper<T, U>): Promise<Option>;
 mapLeft<V>(mapper: Mapper<T, V>): Either<V, null>;
 mapLeftAsync<V>(mapper: AsyncMapper<T, V>): Promise<Either<V, null>>;
 mapRight<V>(mapper: Mapper<null, V>): Either<T, V>;
 mapRightAsync<V>(mapper: AsyncMapper<null, V>): Promise<Either<T, V>>;
 match<V>(onLeft: Mapper<T, V>, onRight: Mapper<null, V>): V;
 matchAsync<V>(onLeft: AsyncMapper<T, V>, onRight: AsyncMapper<null, V>): Promise<V>;
 okOr<E>(error: E | Producer<E>): Result<T, E>;
 okOrAsync<E>(error: E | Promise<E> | AsyncProducer<E>): Promise<Result<T, E>>;
 okOrError(message: string | Producer<string>): Result<T, Error>;
 okOrErrorAsync(message: string | Promise<string> | AsyncProducer<string>): Promise<Result<T, Error>>;
 rightOr(fallback: Mapper<T, null>): null;
 rightOrAsync(fallback: Promise<null> | AsyncMapper<T, null>): Promise<null>;
 tapLeft(callback: Consumer<T>): Either<T, null>;
 tapLeftAsync(callback: AsyncConsumer<T>): Promise<Either<T, null>>;
 tapRight(callback: Consumer<null>): Either<T, null>;
 tapRightAsync(callback: AsyncConsumer<null>): Promise<Either<T, null>>;
 valueOr(fallback: T | Producer<T>): T;
 valueOrAsync(fallback: T | Promise<T> | AsyncProducer<T>): Promise<T>;
}

Type Parameters

Hierarchy (view full)

Either<T, null | undefined>
- Option

Methods

andThen

andThen(mapper): Option
Chains a new Option to the current one if it is Some.
Type Parameters
- U
Parameters
- mapper: Mapper<T, Option>
 The mapper function to apply to the value if it is Some.
Returns Option
A new Option with the mapped value if it is Some, otherwise the value as-is.
Example
```
const object = Option.from({name: "Alice"});
const name = object.andThen(o => Option.from(o.name)); // Some("Alice")
const age = object.andThen(o => Option.from(o.age)); // None
```
- Defined in src/option/option.ts:121

andThenAsync

andThenAsync(mapper): Promise<Option>
Chains a new Option to the current one if it is Some, but asynchronously.
Type Parameters
- U
Parameters
- mapper: AsyncMapper<T, Option>
 The async mapper function to apply to the value if it is Some.
Returns Promise<Option>
A new Option with the mapped value if it is Some, otherwise the value as-is.
Example
```
// const userId: Option<number>;
const url = userId.map(n => `https://api.example.com/users/${n}`);
const name = await url.andThenAsync(async url => {
 const res = await fetch(url));
 const userObj = await res.json();
 return Option.from(userObj.name);
}); // Some("Alice")
```
- Defined in src/option/option.ts:140

getLeftOrThrow

getLeftOrThrow(): T
Returns the value if it is a Left, otherwise throws an error.

NOTE: This function is unsafe and should only be used for testing.

Returns T
The value if it is a Left.

Throws
GetValueError if the value is a Right.
Inherited from Either.getLeftOrThrow
- Defined in src/either/either.ts:340

getRightOrThrow

getRightOrThrow(): null
Returns the value if it is a Right, otherwise throws an error.

NOTE: This function is unsafe and should only be used for testing.

Returns null
The value if it is a Right.

Throws
GetValueError if the value is a Left.
Inherited from Either.getRightOrThrow
- Defined in src/either/either.ts:350

isLeft

isLeft(): boolean
Checks if the value is a Left.

Returns boolean
true if the value is a Left, false otherwise.
Example
```
const value = Either.left(42);
value.isLeft(); // => true
```
Inherited from Either.isLeft
- Defined in src/either/either.ts:23

isNone

isNone(): boolean

Checks if the value is None.

Returns boolean

true if the value is None, false otherwise.

Example

const something = Option.from(123);
something.isNone(); // false

const nothing = Option.from(null);
nothing.isNone(); // true

isRight

isRight(): boolean
Checks if the value is a Right.

Returns boolean
true if the value is a Right, false otherwise.
Example
```
const value = Either.right(42);
value.isRight(); // => true
```
Inherited from Either.isRight
- Defined in src/either/either.ts:36

isSome

isSome(): boolean

Checks if the value is Some.

Returns boolean

true if the value is Some, false otherwise.

Example

const something = Option.from(123);
something.isSome(); // true

const nothing = Option.from(null);
nothing.isSome();

leftOr

leftOr(fallback): T
Returns the value if it is a Left, otherwise returns a default value.
Parameters
- fallback: T | Mapper<null, T>
 The default value (as-is or produced from a callback) to return if the value is a Right.
Returns T
The value if it is a Left, otherwise the default value.
Example
```
const value = Either.left(42);
value.leftOr(0); // => 42
```
Example
```
const value = Either.right(42);
value.leftOr(0); // => 0
```
Inherited from Either.leftOr
- Defined in src/either/either.ts:56

leftOrAsync

leftOrAsync(fallback): Promise<T>
Returns the value if it is a Left, otherwise returns a default value asynchronously.
Parameters
- fallback: T | Promise<T> | AsyncMapper<null, T>
 The default value (as-is or produced from a callback) to return if the value is a Right.
Returns Promise<T>
The value if it is a Left, otherwise the default value.
Example
```
const value = Either.left(42);
await value.leftOrAsync(async () => Promise.resolve(0)); // => 42
```
Example
```
const value = Either.right(42);
await value.leftOrAsync(async () => Promise.resolve(0)); // => 0
```
Inherited from Either.leftOrAsync
- Defined in src/either/either.ts:76

map

map(mapper): Option
Maps the value if it is Some.
Type Parameters
- U
Parameters
- mapper: Mapper<T, U>
 The mapper function to apply to the value if it is Some.
Returns Option
A new Option with the mapped value if it is Some, otherwise the Option as-is.
Example
```
const something = Option.from(123);
something.map(n => n.toString()); // Some("123")
```
- Defined in src/option/option.ts:92

mapAsync

mapAsync(mapper): Promise<Option>
Maps the value if it is Some, but asynchronously.
Type Parameters
- U
Parameters
- mapper: AsyncMapper<T, U>
 The async mapper function to apply to the value if it is Some.
Returns Promise<Option>
A new Option with the mapped value if it is Some, otherwise the Option as-is.
Example
```
const something = Option.from("https://example.com");
something.mapAsync(async url => await fetch(url)); // Promise(Some(Response))
```
- Defined in src/option/option.ts:106

mapLeft

mapLeft<V>(mapper): Either<V, null>
Maps the value if it is a Left, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: Mapper<T, V>
 The function to apply to the value if it is a Left.
Returns Either<V, null>
A new Either with the mapped value if it is a Left, otherwise the value as-is.
Example
```
const value = Either.left(1);
value.mapLeft((value) => value + 1); // => Left(2)
```
Example
```
const value = Either.right(1);
value.mapLeft((value) => value + 1); // => Right(1)
```
Inherited from Either.mapLeft
- Defined in src/either/either.ts:136

mapLeftAsync

mapLeftAsync<V>(mapper): Promise<Either<V, null>>
Maps the value if it is a Left asynchronously, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: AsyncMapper<T, V>
 The async function to apply to the value if it is a Left.
Returns Promise<Either<V, null>>
A new Either with the mapped value if it is a Left, otherwise the value as-is.
Example
```
const value = Either.left(1);
await value.mapLeftAsync(async (value) => Promise.resolve(value + 1)); // => Left(2)
```
Example
```
const value = Either.right(1);
await value.mapLeftAsync(async (value) => Promise.resolve(value + 1)); // => Right(1)
```
Inherited from Either.mapLeftAsync
- Defined in src/either/either.ts:156

mapRight

mapRight<V>(mapper): Either<T, V>
Maps the value if it is a Right, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: Mapper<null, V>
 The function to apply to the value if it is a Right.
Returns Either<T, V>
A new Either with the mapped value if it is a Right, otherwise the value as-is.
Example
```
const value = Either.right(1);
value.mapRight((value) => value + 1); // => Right(2)
```
Example
```
const value = Either.left(1);
value.mapRight((value) => value + 1); // => Left(1)
```
Inherited from Either.mapRight
- Defined in src/either/either.ts:176

mapRightAsync

mapRightAsync<V>(mapper): Promise<Either<T, V>>
Maps the value if it is a Right asynchronously, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: AsyncMapper<null, V>
 The async function to apply to the value if it is a Right.
Returns Promise<Either<T, V>>
A new Either with the mapped value if it is a Right, otherwise the value as-is.
Example
```
const value = Either.right(1);
await value.mapRightAsync(async (value) => Promise.resolve(value + 1)); // => Right(2)
```
Example
```
const value = Either.left(1);
await value.mapRightAsync(async (value) => Promise.resolve(value + 1)); // => Left(1)
```
Inherited from Either.mapRightAsync
- Defined in src/either/either.ts:196

match

match<V>(onLeft, onRight): V
Matches the jonad by calling the appropriate callback based on the value type.
Type Parameters
- V
Parameters
- onLeft: Mapper<T, V>
 If the value is a Left, this callback is called with the value.
- onRight: Mapper<null, V>
 If the value is a Right, this callback is called with the value.
Returns V
The result of the callback that was called.
Example
```
const value = Either.left(42);
value.match(
 (lvalue) => console.log(`Answer to life: ${lvalue}`),
 (rvalue) => console.log(`Hello, ${rvalue}`)
); // => "Answer to life: 42"
```
Example
```
const value = Either.right("world!");
value.match(
 (value) => console.log(`Answer to life: ${lvalue}`),
 (value) => console.log(`Hello, ${rvalue}`)
); // => "Hello, world!"
```
Inherited from Either.match
- Defined in src/either/either.ts:303

matchAsync

matchAsync<V>(onLeft, onRight): Promise<V>
Matches the jonad by calling the appropriate callback based on the value type asynchronously.
Type Parameters
- V
Parameters
- onLeft: AsyncMapper<T, V>
 If the value is a Left, this callback is called with the value.
- onRight: AsyncMapper<null, V>
 If the value is a Right, this callback is called with the value.
Returns Promise<V>
The result of the callback that was called.
Example
```
const value = Either.left(1);
await value.matchAsync(
 async (lvalue) => `${lvalue} + 2 = ${lvalue + 2}`,
 async (rvalue) => `1 + ${rvalue} = ${1 + rvalue}`
); // => "1 + 2 = 3"
```
Example
```
const value = Either.right(2);
await value.matchAsync(
 async (lvalue) => `${lvalue} + 2 = ${lvalue + 2}`,
 async (rvalue) => `1 + ${rvalue} = ${1 + rvalue}`
); // => "1 + 2 = 3"
```
Inherited from Either.matchAsync
- Defined in src/either/either.ts:330

okOr

okOr<E>(error): Result<T, E>
Maps the Option to a Result.

If the Option is Some, the value will be wrapped in an Ok. If the Option is None, the provided error will be returned.
Type Parameters
- E extends Error
Parameters
- error: E | Producer<E>
 The error to return if the Option is None.
Returns Result<T, E>
A Result of the Option.
Example
```
const something = Option.from(123);
something.okOr(new Error("Value is None")); // Ok(123)

const nothing = Option.none();
nothing.okOr(new Error("Value is None")); // Err(Error("Value is None"))
```
- Defined in src/option/option.ts:159

okOrAsync

okOrAsync<E>(error): Promise<Result<T, E>>
Maps the Option to a promised Result.

If the Option is Some, the value will be wrapped in an Ok. If the Option is None, the provided error will be returned.
Type Parameters
- E extends Error
Parameters
- error: E | Promise<E> | AsyncProducer<E>
 The error to return if the Option is None.
Returns Promise<Result<T, E>>
A Result of the Option.
Example
```
const something = Option.from(123);
something.okOrAsync(async () => {
 await error_reporter.send("error", "Value is None");
 return new Error("Value is None");
}); 
```
- Defined in src/option/option.ts:178

okOrError

okOrError(message): Result<T, Error>
Maps the Option to a Result, creating a new error from the message if the Option is None.
Parameters
- message: string | Producer<string>
 The message to create the error from if the Option is None.
Returns Result<T, Error>
A Result of the Option.
Example
```
const something = Option.from(123);
something.okOrError("Value is None"); // Ok(123)

const nothing = Option.none();
nothing.okOrError("Value is None"); // Err(Error("Value is None"))
```
- Defined in src/option/option.ts:195

okOrErrorAsync

okOrErrorAsync(message): Promise<Result<T, Error>>
Maps the Option to a promised Result, creating a new error from the message if the Option is None.
Parameters
- message: string | Promise<string> | AsyncProducer<string>
 The message to create the error from if the Option is None.
Returns Promise<Result<T, Error>>
A Result of the Option.
Example
```
const something = Option.from(123);
something.okOrErrorAsync(async () => {
 await error_reporter.send("error", "Value is None");
 return "Value is None";
}); // Promise(Ok(123))
```
- Defined in src/option/option.ts:212

rightOr

rightOr(fallback): null
Returns the value if it is a Right, otherwise returns a default value.
Parameters
- fallback: Mapper<T, null>
 The default value (as-is or produced from a callback) to return if the value is a Left.
Returns null
The value if it is a Right, otherwise the default value.
Example
```
const value = Either.right(42);
value.rightOr(0); // => 42
```
Example
```
const value = Either.left(42);
value.rightOr(0); // => 0
```
Inherited from Either.rightOr
- Defined in src/either/either.ts:96

rightOrAsync

rightOrAsync(fallback): Promise<null>
Returns the value if it is a Right, otherwise returns a default value asynchronously.
Parameters
- fallback: Promise<null> | AsyncMapper<T, null>
 The default value (as-is or produced from a callback) to return if the value is a Left.
Returns Promise<null>
The value if it is a Right, otherwise the default value.
Example
```
const value = Either.right(42);
await value.rightOrAsync(async () => Promise.resolve(0)); // => 42
```
Example
```
const value = Either.left(42);
await value.rightOrAsync(async () => Promise.resolve(0)); // => 0
```
Inherited from Either.rightOrAsync
- Defined in src/either/either.ts:116

tapLeft

tapLeft(callback): Either<T, null>
Applies a function to the value if it is a Left, returning itself.
Parameters
- callback: Consumer<T>
 The function to apply to the value if it is a Left.
Returns Either<T, null>
The Either as-is.
Example
```
const value = Either.left([1, 2]);
value.tapLeft((value) => value.push(3)); // => Left([1, 2, 3])
```
Example
```
const value = Either.right([1, 2]);
value.tapLeft((value) => value.push(3)); // => Right([1, 2])
```
Inherited from Either.tapLeft
- Defined in src/either/either.ts:216

tapLeftAsync

tapLeftAsync(callback): Promise<Either<T, null>>
Asynchronously applies a function to the value if it is a Left, returning itself.
Parameters
- callback: AsyncConsumer<T>
 The async function to apply to the value if it is a Left.
Returns Promise<Either<T, null>>
The Either as-is.
Example
```
const value = Either.left([1, 2]);
await value.tapLeftAsync(async (value) => value.push(3)); // => Left([1, 2, 3])
```
Example
```
const value = Either.right([1, 2]);
await value.tapLeftAsync(async (value) => value.push(3)); // => Right([1, 2])
```
Inherited from Either.tapLeftAsync
- Defined in src/either/either.ts:236

tapRight

tapRight(callback): Either<T, null>
Applies a function to the value if it is a Right, returning itself.
Parameters
- callback: Consumer<null>
 The function to apply to the value if it is a Right.
Returns Either<T, null>
The Either as-is.
Example
```
const value = Either.right([1, 2]);
value.tapRight((value) => value.push(3)); // => Right([1, 2, 3])
```
Example
```
const value = Either.left([1, 2]);
value.tapRight((value) => value.push(3)); // => Left([1, 2])
```
Inherited from Either.tapRight
- Defined in src/either/either.ts:256

tapRightAsync

tapRightAsync(callback): Promise<Either<T, null>>
Asynchronously applies a function to the value if it is a Right, returning itself.
Parameters
- callback: AsyncConsumer<null>
 The async function to apply to the value if it is a Right.
Returns Promise<Either<T, null>>
The Either as-is.
Example
```
const value = Either.right([1, 2]);
await value.tapRightAsync(async (value) => value.push(3)); // => Right([1, 2, 3])
```
Example
```
const value = Either.left([1, 2]);
await value.tapRightAsync(async (value) => value.push(3)); // => Left([1, 2])
```
Inherited from Either.tapRightAsync
- Defined in src/either/either.ts:276

valueOr

valueOr(fallback): T
Returns the value if it is Some, otherwise returns a default value.
Parameters
- fallback: T | Producer<T>
 The default value (as-is or produced from a callback) to return if the value is None.
Returns T
The value if it is Some, otherwise the default value.
Example
```
const something = Option.from(123);
something.valueOr(0); // 123

const nothing = Option.none();
nothing.valueOr(0); // 0
```
- Defined in src/option/option.ts:61

valueOrAsync

valueOrAsync(fallback): Promise<T>
Returns the value if it is Some, otherwise returns a default value asynchronously.
Parameters
- fallback: T | Promise<T> | AsyncProducer<T>
 The default value (as-is or produced from a callback) to return if the value is None.
Returns Promise<T>
The value if it is an Ok, otherwise the default value.
Example
```
const something = Option.from(123);
something.valueOrAsync(async () => 0); // 123

const nothing = Option.none();
nothing.valueOrAsync(async () => 0); // 0
```
- Defined in src/option/option.ts:78

Interface Option<T>

Type Parameters

Hierarchy (view full)

Index

Methods

Methods

andThen

Type Parameters

Parameters

Returns Option<U>

Example

andThenAsync

Type Parameters

Parameters

Returns Promise<Option<U>>

Example

getLeftOrThrow

Returns T

Throws

getRightOrThrow

Returns null

Throws

isLeft

Returns boolean

Example

isNone

Returns boolean

Example

isRight

Returns boolean

Example

isSome

Returns boolean

Example

leftOr

Parameters

Returns T

Example

Example

leftOrAsync

Parameters

Returns Promise<T>

Example

Example

map

Type Parameters

Parameters

Returns Option<U>

Example

mapAsync

Type Parameters

Parameters

Returns Promise<Option<U>>

Example

mapLeft

Type Parameters

Parameters

Returns Either<V, null>

Example

Example

mapLeftAsync

Type Parameters

Parameters

Returns Promise<Either<V, null>>

Example

Example

mapRight

Type Parameters

Parameters

Returns Either<T, V>

Example

Example

mapRightAsync

Type Parameters

Parameters

Returns Promise<Either<T, V>>

Example

Example

match

Type Parameters