Does for comprehension have something like "flatYield"?

Question

I have some code like

//all data have different types
val data1Future = loadData1(params)
val data2Future = loadData2(params)
val data3Future = loadData3(params)

def saveResult(rez): Future[_] = ???

data1Future.flatMap { data1 =>
  data2Future.flatMap { data2 =>
    data3Future.flatMap { data3 =>
      //do some computation
      //several rows and several vals
      val rez = ???
      saveResult(rez)
   }
  }
}

But it is a litle bit ugly :) Unfortunatelly, I can't use for comprehension since I need something like "flatYield"

for {
  data1 <- data1Future
  data1 <- data1Future
  data1 <- data1Future
} flatYield {
  //do some computation
  //several rows and several vals
  val rez = data1 + data2 + data3
  saveResult(rez)
}

Do you know pattern that is such elegant as "for comprehension" but with flatMap instead of map at the end of the chain?

Answer 1

You can do this:

for {
  data1 <- data1Future
  data2 <- data2Future
  data3 <- data3Future
  rez = {
    //do some computation
    //several rows and several vals
    data1 + data2 + data3
  }
  r <- saveResult(rez)
} yield r

This translates to

data1Future.flatMap { data1 =>
  data2Future.flatMap { data2 =>
    data3Future.flatMap { data3 =>
      val rez = {
        //do some computation
        //several rows and several vals
        data1 + data2 + data3
      }
      saveResult(rez).map(r => r)
    }
  }
}

which is isomorphic to your code.