byethrow

    Function: mapError()

    Applies a transformation function to the error value of a Result or ResultAsync. If the input is a Success, it will be returned unchanged.

    Type Param

    The input Result or ResultAsync.

    Type Param

    The transformed error value type.

    Examples

    import { 
    import Result
    Result     } from '@praha/byethrow';    

const 
    const result: Result.Result<never, Error>
    result     = 
    import Result
    Result    .
    const pipe: <Result.Result<never, "NotFound">, Result.Result<never, Error>>(a: Result.Result<never, "NotFound">, ab: (a: Result.Result<never, "NotFound">) => Result.Result<never, Error>) => Result.Result<never, Error> (+25 overloads)
    pipe    (    
  
    import Result
    Result    .
    const fail: <"NotFound">(error: "NotFound") => Result.Result<never, "NotFound"> (+1 overload)
    fail    ('NotFound'),    
  
    import Result
    Result    .
    const mapError: <Result.Result<never, "NotFound">, Error>(fn: (a: "NotFound") => Error) => (result: Result.Result<never, "NotFound">) => Result.Result<never, Error> (+1 overload)
    mapError    ((
    error: "NotFound"
    error    ) => new 
    var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
    Error    (
    error: "NotFound"
    error    )),    
);
// { type: 'Failure', error: Error('NotFound') }
    import { 
    import Result
    Result     } from '@praha/byethrow';    

const 
    const result: Result.Result<123, Error>
    result     = 
    import Result
    Result    .
    const pipe: <Result.Result<123, never>, Result.Result<123, Error>>(a: Result.Result<123, never>, ab: (a: Result.Result<123, never>) => Result.Result<123, Error>) => Result.Result<123, Error> (+25 overloads)
    pipe    (    
  
    import Result
    Result    .
    const succeed: <123>(value: 123) => Result.Result<123, never> (+1 overload)
    succeed    (123),    
  
    import Result
    Result    .
    const mapError: <Result.Result<123, never>, Error>(fn: (a: never) => Error) => (result: Result.Result<123, never>) => Result.Result<123, Error> (+1 overload)
    mapError    ((
    error: never
    error    ) => new 
    var Error: ErrorConstructor
new (message?: string, options?: ErrorOptions) => Error (+1 overload)
    Error    (
    error: never
    error    )),    
);
// { type: 'Success', value: 123 }

    See

    pipe - It is recommended to use this function with the pipe function for better readability and composability.

    Call Signature

    mapError<R1, E2>(fn): (result) => ResultFor<R1, InferSuccess<R1>, E2>

    Type Parameters

    R1

    R1 extends ResultMaybeAsync<any, any>

    E2

    E2

    Parameters

    fn

    (a) => E2

    Returns

    (result): ResultFor<R1, InferSuccess<R1>, E2>

    Parameters

    result

    R1

    Returns

    ResultFor<R1, InferSuccess<R1>, E2>

    Call Signature

    mapError<E1, E2>(fn): <R1>(result) => ResultFor<R1, InferSuccess<R1>, E2>

    Type Parameters

    E1

    E1

    E2

    E2

    Parameters

    fn

    (a) => E2

    Returns

    <R1>(result): ResultFor<R1, InferSuccess<R1>, E2>

    Type Parameters

    R1

    R1 extends ResultMaybeAsync<any, E1>

    Parameters

    result

    R1

    Returns

    ResultFor<R1, InferSuccess<R1>, E2>