Interface Result<V, E>

A Result jonad, a subtype of Either.

Represents a value ("Ok") or an error ("Err"). Associates a set of utility functions to work with the jonad.

interface Result<V, E> {
    andThen<T>(mapper: Mapper<V, Result<T, E>>): Result<T, E>;
    andThenAsync<T>(mapper: AsyncMapper<V, Result<T, E>>): Promise<Result<T, E>>;
    asNullable(): Result<Option<V>, E>;
    getLeftOrThrow(): V;
    getRightOrThrow(): E;
    isErr(): boolean;
    isLeft(): boolean;
    isOk(): boolean;
    isRight(): boolean;
    leftOr(fallback: V | Mapper<E, V>): V;
    leftOrAsync(fallback: V | Promise<V> | AsyncMapper<E, V>): Promise<V>;
    map<T>(mapper: Mapper<V, T>): Result<T, E>;
    mapAsync<T>(mapper: AsyncMapper<V, T>): Promise<Result<T, E>>;
    mapErr<T>(mapper: Mapper<E, T>): Result<V, T>;
    mapErrAsync<T>(mapper: AsyncMapper<E, T>): Promise<Result<V, T>>;
    mapLeft<V>(mapper: Mapper<V, V>): Either<V, E>;
    mapLeftAsync<V>(mapper: AsyncMapper<V, V>): Promise<Either<V, E>>;
    mapRight<V>(mapper: Mapper<E, V>): Either<V, V>;
    mapRightAsync<V>(mapper: AsyncMapper<E, V>): Promise<Either<V, V>>;
    match<V>(onLeft: Mapper<V, V>, onRight: Mapper<E, V>): V;
    matchAsync<V>(onLeft: AsyncMapper<V, V>, onRight: AsyncMapper<E, V>): Promise<V>;
    rightOr(fallback: E | Mapper<V, E>): E;
    rightOrAsync(fallback: E | Promise<E> | AsyncMapper<V, E>): Promise<E>;
    someOrNone(): Option<V>;
    tapLeft(callback: Consumer<V>): Either<V, E>;
    tapLeftAsync(callback: AsyncConsumer<V>): Promise<Either<V, E>>;
    tapRight(callback: Consumer<E>): Either<V, E>;
    tapRightAsync(callback: AsyncConsumer<E>): Promise<Either<V, E>>;
    valueOr(fallback: V | Mapper<E, V>): V;
    valueOrAsync(fallback: V | Promise<V> | AsyncMapper<E, V>): Promise<V>;
}

Type Parameters

V
E extends Error

Hierarchy (view full)

Either<V, E>
- Result

Methods

andThen

andThen<T>(mapper): Result<T, E>
Chains a new Result to the current one if it is Ok.
Type Parameters
- T
Parameters
- mapper: Mapper<V, Result<T, E>>
  The mapper function to apply to the value if it is an Ok.
Returns Result<T, E>
A new Result with the mapped value if it is an Ok, otherwise the value as-is.
- Defined in src/result/result.ts:151

andThenAsync

andThenAsync<T>(mapper): Promise<Result<T, E>>
Chains a new Result to the current one if it is Ok, but asynchronously.
Type Parameters
- T
Parameters
- mapper: AsyncMapper<V, Result<T, E>>
  The async mapper function to apply to the value if it is an Ok.
Returns Promise<Result<T, E>>
A new Result with the mapped value if it is an Ok, otherwise the value as-is.
- Defined in src/result/result.ts:158

asNullable

asNullable(): Result<Option<V>, E>
Maps the Result so the Ok value is wrapped in an Option based on its presence.

If the Result is an Ok and the value is not null or undefined, then the inner value will become Some. If the Result is an Ok and the value is null or undefined, then the inner value will become None. If the Result is an Err, then nothing will happen.

Returns Result<Option<V>, E>
A new Result with the Ok value wrapped in an Option based on its presence.
- Defined in src/result/result.ts:180

getLeftOrThrow

getLeftOrThrow(): V
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 V
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(): E
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 E
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

isErr

isErr(): boolean

Checks if the value is an Err.

Returns boolean

true if the value is an Err, false otherwise.

Example

const okish = Result.ok(123);
okish.isErr(); // false

const errish = Resulr.error("An error");
errish.isErr(); // true

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

isOk

isOk(): boolean

Checks if the value is an Ok.

Returns boolean

true if the value is an Ok, false otherwise.

Example

const okish = Result.ok(123);
result.isOk(); // true

const errish = Resulr.error("An error");
result.isOk(); // false

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

leftOr

leftOr(fallback): V
Returns the value if it is a Left, otherwise returns a default value.
Parameters
- fallback: V | Mapper<E, V>
  The default value (as-is or produced from a callback) to return if the value is a Right.
Returns V
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<V>
Returns the value if it is a Left, otherwise returns a default value asynchronously.
Parameters
- fallback: V | Promise<V> | AsyncMapper<E, V>
  The default value (as-is or produced from a callback) to return if the value is a Right.
Returns Promise<V>
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<T>(mapper): Result<T, E>
Maps the value if it is an Ok.
Type Parameters
- T
Parameters
- mapper: Mapper<V, T>
  The mapper function to apply to the value if it is an Ok.
Returns Result<T, E>
A new Result with the mapped value if it is an Ok, otherwise the result as-is.
Example
```
const okish = Result.ok(123);
okish.map(value => value * 2); // Ok(246)

const errish = Resulr.error("An error");
errish.map(value => value * 2); // Err("An error")
```
- Defined in src/result/result.ts:94

mapAsync

mapAsync<T>(mapper): Promise<Result<T, E>>
Maps the value if it is an Ok, but asynchronously.
Type Parameters
- T
Parameters
- mapper: AsyncMapper<V, T>
  The async mapper function to apply to the value if it is an Ok.
Returns Promise<Result<T, E>>
A new Result with the mapped value if it is an Ok, otherwise the result as-is.
Example
```
const okish = Result.ok(123);
okish.mapAsync(async value => value * 2); // Promise(246)

const errish = Resulr.error("An error");
errish.mapAsync(async value => value * 2); 
```
- Defined in src/result/result.ts:110

mapErr

mapErr<T>(mapper): Result<V, T>
Maps the error if it is an Err, otherwise returns the error as-is.
Type Parameters
- T extends Error
Parameters
- mapper: Mapper<E, T>
  The mapper function to apply to the error if it is an Err.
Returns Result<V, T>
A new Result with the mapped error if it is an Err, otherwise the result as-is.
Example
```
const okish = Result.ok(123);
okish.mapErr(error => new Error("An error")); // Ok(123)

const errish = Resulr.error("An error");
errish.mapErr(error => new Error("Another error")); 
```
- Defined in src/result/result.ts:126

mapErrAsync

mapErrAsync<T>(mapper): Promise<Result<V, T>>
Maps the error if it is an Err, but asynchronously.
Type Parameters
- T extends Error
Parameters
- mapper: AsyncMapper<E, T>
  The async mapper function to apply to the error if it is an Err.
Returns Promise<Result<V, T>>
A new Result with the mapped error if it is an Err, otherwise the result as-is.
Example
```
const okish = Result.ok(123);
okish.mapErrAsync(async error => new Error("An error")); // Ok(123)

const errish = Resulr.error("An error");
errish.mapErrAsync(async error => new Error("Another error")); // Promise(Err("Another error"))
```
- Defined in src/result/result.ts:143

mapLeft

mapLeft<V>(mapper): Either<V, E>
Maps the value if it is a Left, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: Mapper<V, V>
  The function to apply to the value if it is a Left.
Returns Either<V, E>
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, E>>
Maps the value if it is a Left asynchronously, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: AsyncMapper<V, V>
  The async function to apply to the value if it is a Left.
Returns Promise<Either<V, E>>
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<V, V>
Maps the value if it is a Right, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: Mapper<E, V>
  The function to apply to the value if it is a Right.
Returns Either<V, 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<V, V>>
Maps the value if it is a Right asynchronously, otherwise returns the value as-is.
Type Parameters
- V
Parameters
- mapper: AsyncMapper<E, V>
  The async function to apply to the value if it is a Right.
Returns Promise<Either<V, 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<V, V>
  If the value is a Left, this callback is called with the value.
- onRight: Mapper<E, 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<V, V>
  If the value is a Left, this callback is called with the value.
- onRight: AsyncMapper<E, 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

rightOr

rightOr(fallback): E
Returns the value if it is a Right, otherwise returns a default value.
Parameters
- fallback: E | Mapper<V, E>
  The default value (as-is or produced from a callback) to return if the value is a Left.
Returns E
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<E>
Returns the value if it is a Right, otherwise returns a default value asynchronously.
Parameters
- fallback: E | Promise<E> | AsyncMapper<V, E>
  The default value (as-is or produced from a callback) to return if the value is a Left.
Returns Promise<E>
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

someOrNone

someOrNone(): Option<V>
Maps the Result into an Option.

If the Result is an Ok and the value is not null or undefined, then it will be Some with that value. If the Result is an Ok and the value is null or undefined, then it will be None. If the Result is an Err, then it will be None with the error discarded.

Returns Option<V>
Some if the value is Ok and present, otherwise None.
- Defined in src/result/result.ts:169

tapLeft

tapLeft(callback): Either<V, E>
Applies a function to the value if it is a Left, returning itself.
Parameters
- callback: Consumer<V>
  The function to apply to the value if it is a Left.
Returns Either<V, E>
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<V, E>>
Asynchronously applies a function to the value if it is a Left, returning itself.
Parameters
- callback: AsyncConsumer<V>
  The async function to apply to the value if it is a Left.
Returns Promise<Either<V, E>>
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<V, E>
Applies a function to the value if it is a Right, returning itself.
Parameters
- callback: Consumer<E>
  The function to apply to the value if it is a Right.
Returns Either<V, E>
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<V, E>>
Asynchronously applies a function to the value if it is a Right, returning itself.
Parameters
- callback: AsyncConsumer<E>
  The async function to apply to the value if it is a Right.
Returns Promise<Either<V, E>>
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): V
Returns the value if it is an Ok, otherwise returns a default value.
Parameters
- fallback: V | Mapper<E, V>
  The default value (as-is or produced from a callback) to return if the value is an Err.
Returns V
The value if it is an Ok, otherwise the default value.
Example
```
const okish = Result.ok(123);
okish.valueOr(0); // 123

const errish = Resulr.error("An error");
errish.valueOr(0); 
```
- Defined in src/result/result.ts:60

valueOrAsync

valueOrAsync(fallback): Promise<V>
Returns the value if it is an Ok, otherwise returns a default value asynchronously.
Parameters
- fallback: V | Promise<V> | AsyncMapper<E, V>
  The default value (as-is or produced from a callback) to return if the value is an Err.
Returns Promise<V>
The value if it is an Ok, otherwise the default value.
Example
```
const okish = Result.ok(123);
okish.valueOrAsync(async () => 0); // Promise(123)

const errish = Resulr.error("An error");
errish.valueOrAsync(Promise.resolve(0)); // Promise(0)
```
- Defined in src/result/result.ts:77

Interface Result<V, E>

Type Parameters

Hierarchy (view full)

Index

Methods

Methods

andThen

Type Parameters

Parameters

Returns Result<T, E>

andThenAsync

Type Parameters

Parameters

Returns Promise<Result<T, E>>

asNullable

Returns Result<Option<V>, E>

getLeftOrThrow

Returns V

Throws

getRightOrThrow

Returns E

Throws

isErr

Returns boolean

Example

isLeft

Returns boolean

Example

isOk

Returns boolean

Example

isRight

Returns boolean

Example

leftOr

Parameters

Returns V

Example

Example

leftOrAsync

Parameters

Returns Promise<V>

Example

Example

map

Type Parameters

Parameters

Returns Result<T, E>

Example

mapAsync

Type Parameters

Parameters

Returns Promise<Result<T, E>>

Example

mapErr

Type Parameters

Parameters

Returns Result<V, T>

Example

mapErrAsync

Type Parameters

Parameters

Returns Promise<Result<V, T>>

Example

mapLeft

Type Parameters

Parameters

Returns Either<V, E>

Example

Example

mapLeftAsync

Type Parameters

Parameters

Returns Promise<Either<V, E>>

Example

Example

mapRight

Type Parameters

Parameters

Returns Either<V, V>