for comprehension trying to use map (rather than flatMap)

map3.scala

object TestForComprehensionMap3 {

  def map3(a: Option[Int], b: Option[Int], c: Option[Int])(f: (Int, Int, Int) => Option[Int]): Option[Int] = {
	a.flatMap(x => b.flatMap(y => c.flatMap(z => f(x,y,z) ) ) )
  }

  def map3ForExpr(a: Option[Int], b: Option[Int], c: Option[Int])(f: (Int, Int, Int) => Option[Int]): Option[Int] = {
	for { 
		x <- a
		y <- b
		z <- c
  	} yield( f(x,y,z))
  }  

  def main(args: Array[String]) {
  	val mapResult = map3(Some(1), Some(2), Some(3))( (x,y,z) => Some(x*y*z) )
  	assert(mapResult == Some(6))

	val forResult = map3ForExpr(Some(1), Some(2), Some(3))( (x,y,z) => Some(x*y*z) )
	assert(forResult == Some(6))
  } 
}


/* compile-time error:

C:\Users\Kevin\Workspace\side-work>scalac TestForComprehensionMap3.scala && scala TestForComprehensionMap3
TestForComprehensionMap3.scala:13: error: type mismatch;
 found   : Option[Int]
 required: Int
        } yield( f(x,y,z))//yield out
                  ^
one error found

*/