Idiomatic Arrow

Question

I have the following method:

internal typealias MaybeError<T> = Either<GenericError, T>

override fun createCompany(companyDomain: CompanyDomain): MaybeError<CompanyDomain> =
    checkCompany(companyDomain).map { it.toEntity() }.fold({ Either.left(it) }) { company ->
        with (companyRepository) {
            isCompanyExists(company).fold({ Either.left(it) }) { isExists ->
                if (isExists) return@with Either.left(CompanyNameExists(companyDomain))
                createCompany(company).fold({ Either.right(companyDomain) }) { Either.left(it) }
            }
        }
    }

Is there a better/more idiomatic way to write this using Arrow?

Have you tried using `flatMap` instead of `fold` for the cases where the left is respected? — MLProgrammer-CiM, May 16 '19 at 19:59

score 1 · Accepted Answer · answered May 17 '19 at 06:50

It is hard to refactor because I can only assume what used methods should return. But I guess the methods returns MaybeError. In this case we can omit fold({ Either.left(it) }) and we can use map or flatMap.

internal typealias MaybeError<T> = Either<GenericError, T>

override fun createCompany(companyDomain: CompanyDomain): MaybeError<CompanyDomain> =
    checkCompany(companyDomain)
        .map { it.toEntity() }
        .flatMap { company ->
            companyRepository.isCompanyExists(company)
                .flatMap { isExists ->
                    if (isExists) {
                        MaybeError.left(CompanyNameExists(companyDomain))
                    } else {
                        companyRepository.createCompany(company)
                    }
                }
        }

Correct, the methods do return `MaybeError`. Looks great, thanks! — m0skit0, May 17 '19 at 08:08

Idiomatic Arrow

1 Answers1