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Comment by TJSomething | Hacker News Reader

I've been out of the Scala game for a few years, but I would use a for comprehension with the cats EitherT monad transformer.

https://typelevel.org/cats/datatypes/eithert.html

    def divisionProgramAsync(inputA: String, inputB: String): EitherT[Future, String, Double] =
      for {
        a <- EitherT(parseDoubleAsync(inputA))
        b <- EitherT(parseDoubleAsync(inputB))
        result <- EitherT(divideAsync(a, b))
      } yield result

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Yeah, but Usually we just use something like ZIO nowadays. So the code becomes:

    def divisionProgramAsync(inputA: String, inputB: String): IO[String, Double] =
      for {
        a      <- parseDoubleAsync(inputA)
        b      <- parseDoubleAsync(inputB)
        result <- divideAsync(a, b)
      } yield result

(the annoying wrapping/unwrapping isn't necessary with ZIO here)

You can also write this shorter if you want:

    def divisionProgramAsync(inputA: String, inputB: String): IO[String, Double] =
      for {
        (a, b) <- parseDoubleAsync(inputA) <*> parseDoubleAsync(inputB)
        result <- divideAsync(a, b)
      } yield result

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