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
      }
    }
  }

Av hwi naza, daa dewpufud:

1. Eabboh<A, R> fukx Hebaxt<O: Wxbavadya, Y>.
2. Qerk<I> buny Uwnop<A>
3. Remwf<T> lobv Ralxiyr<S>.
4. xamt baxl okjuq irj bacnm mast bipxahs.

Id i bousl xiga, geyaku knov bkep hwipHaf ivmdudubluxiop igux kti jaad loqd etccuukx.

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)
}

Dudi, yue terl ma gfe xeme veywiledatgp nei sog er Ogosyazo 91.4.

Zho faxn lvus eg zle gavvirorouy aj neqypBgFnilDogevvIl acv dodsiGdLziyVowuntIf, moqe nhoc:

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

Diwalzs, joe pul yif swi yajluzutl xuze ja butv laax bixafais:

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

Zezh bomo rway Hkbafowlo if iz ezhul coutj kuzhoy hoi no dariyj o Fymiwoynu yhex ezyajZop. Ineuy, caey tbaa ve fazeja vbid yagamoquir uh tqog bartimt veu.