fp-ts如何处理具有不同权限类型的多个

Question

当Promises的右侧不能很好地对齐时，处理Eithers的Eithers的最佳方法是什么？在这个场景中，我有三个非依赖的“先决条件”操作，表示为Eithers (具有不同的右手类型)。如果它们都成功了，我就不会继续第四个操作了。如果三个操作中的任何一个失败，我都不想继续执行第四个操作。

在这一点上，我有一个解决方案编译，但对可读性不满意。在这种情况下，肯定有更好的方法来处理多个Either？

    //promise of Either<ApiError, CustomerDTO>
    const customer = this.customerService.createCustomer(siteOrigin, createCustReq);

    //promise of Either<ApiError, LocationDTO>
    const location = this.locationService.getRetailOnlineLocation(siteOrigin);

    //promise of Either<ApiError, StationDTO>
    const station = this.stationService.getRetailOnlineStation(siteOrigin);
    
    //execute previous concurrently
    const locationAndStationAndCustomer = await Promise.all([location, station, customer]);

    const locationE = locationAndStationAndCustomer[0];
    const stationE = locationAndStationAndCustomer[1];
    const customerE = locationAndStationAndCustomer[2];


    //How to make this better?
    const stationAndLocationAndCustomer = E.fold(
      (apiErr: ApiError) => E.left(apiErr),
      (location: LocationDTO) => {
        return E.fold(
          (apiErr: ApiError) => E.left(apiErr),
          (station: StationDTO) =>
            E.right(
              E.fold(
                (err: ApiError) => E.left(err),
                (customer: CustomerDTO) =>
                  E.right({ location, station, customer })
              )(customerE)
            )
        )(stationE);
      }
    )(locationE);

Answer 1

我认为这些评论越来越接近正确的答案。sequenceT是解决这类问题的正确方法。

import { sequenceT } from 'fp-ts/Apply'
import * as E from 'fp-ts/Either';

const seq = sequenceT(E.Apply);

return pipe(
  await Promise.all([location, station, customer]),
  seq, // [Either<...>, Either<...>, Either<...>] => Either<ApiError, [...]>
  // map is a bit less cumbersome. If the value was Left it returns Left
  // otherwise it calls the function which returns a new Right value from
  // what the function returns
  E.map(([loc, sta, cust]) => ({
    location: loc,
    station: sta,
    customer: cust,
  })), 
);