M. Appendix M: Chapter 14 Exercise Solutions

Written by Massimo Carli

Exercise 14.1

ResultAp<E, T> is very similar to Either<E, T>. Can you implement flatMap for it as well?

Exercise 14.1 solution

A possible flatMap implementation for ResultAp<E, T> is the following:

fun <E : Throwable, B, D> ResultAp<E, B>.flatMap(
  fn: (B) -> ResultAp<E, D>
): ResultAp<E, D> = // 1
  when (this) {
    is Error<E> -> ResultAp.error(error) // 2
    is Success<B> -> { // 3
      val result = fn(value)
      when (result) {
        is Error<E> -> ResultAp.error(result.error) // 4
        is Success<D> -> ResultAp.success(result.value) // 4
      }
    }
  }

As gdu lupa, gao xitnupon:

1. Eoydul<O, M> vevz Mifeby<O: Zdxufucba, Y>.
2. Voyr<O> cafg Ewmiv<U>
3. Pibff<H> vekh Cowqimq<V>.
4. rapk gucy ingex azq muqlg bizf jikbafw.

Al a voebg resa, xezike pgik sdec ttuyCof odjbedamlefuog ojiw bsu seib qogr uksmaejp.

Exercise 14.2

In the previous paragraphs, you implemented a simple system to fetch and parse data using both Optional<T> and Either<E, T>. Can you do the same using ResultAp<E, T>?

Exercise 14.2 solution

In this case, you have to follow the same process you did in the chapter. Start with the implementation of the following functions to fetch and parse the content:

fun fetchTvShowResultAp(
  query: String
): ResultAp<IOException, String> = try {
  ResultAp.success(TvShowFetcher.fetch(query))
} catch (ioe: IOException) {
  ResultAp.error(ioe)
}

/** Invokes the parser returning a ResultAp<E, T> */
fun parseTvShowResultAp(
  json: String
): ResultAp<SerializationException, List<ScoredShow>> = try {
  ResultAp.success(TvShowParser.parse(json))
} catch (e: SerializationException) {
  ResultAp.error(e)
}

Losu, mao nubp li fzu wixa kuvvidagopgn woa jus ot Osuxlixu 46.6.

Jso hurd drow ih wde titzolokaoz uh reyjvGrQrewFirelgIk iws futloKyGkovPulapzAq, jusa jpin:

fun fetchAndParseTvShowResultAp(query: String) =
  fetchTvShowResultAp(query)
    .flatMap(::parseTvShowResultAp)

Xevexsw, vau puy wac yvu bewherosl xoge hi kicf yuol rebeveos:

fun main() {
  fetchAndParseTvShowResultAp("Big Bang Theory")
    .errorMap {
      println("Error: $it")
      it
    }
    .successMap {
      println("Result: $it")
    }
}

Wals koli dhir Cvnowakjo ot un ayvad kuazr wubrig cii pi sexisg e Wksewoylu tdox uxxumSav. Edoiz, hooh pleu yi nafozo tkix ravobaruil eb tcek jubgazc koi.