byethrow
  • English

      • 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

      R1

      The input Result or ResultAsync.

      Type Param

      E2

      The transformed error value type.

      Examples

      Failure Case (unchanged)

      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') }

      Success Case (unchanged)

      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>

      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>