EitherCallAdapterFactory

A CallAdapter.Factory which supports suspend + Either as the return type

Adding this to Retrofit will enable you to return Either from your service methods.

import arrow.core.Either
import retrofit2.http.GET

data class User(val name: String)
data class ErrorBody(val msg: String)
interface MyService {
  @GET("/user/me")
  suspend fun user(): Either<ErrorBody, User>

  @GET("/user/me")
  suspend fun userResponse(): Either<ErrorBody, User>
}

Using Either as the return type means that 200 status code and HTTP errors return a value, other exceptions will throw.

ResponseE is similar to retrofit2.Response but uses Either for the response body.