Question

I was reading this blog post and i was not able to understand a part of the code.

object O {
  def maximum(x: List[Int]): Int = x match {
  case Nil => error("maximum undefined for empty list")
  case x :: y :: ys => maximum((if(x > y) x else y) :: ys)
  case x :: _ => x
 }
}

Please explain the code maximum((if(x > y) x else y) :: ys)

How the if condition can be a part of the method maximum ?
I understand that if condition is not exactly a parameter.

Answer 1

In Scala, if is an expression, not a statement.

Try this in the REPL:

scala> val x=1; val y=0
x: Int = 1
y: Int = 0

scala> val test=if(x > y) x else y
test: Int = 1

if evaluates to 1 and 1 is assigned to test. In Java if could be expressed with the conditional operator (x > y) ? x : y

Now, you have a function called maximum that takes a List[Int] as a parameter.
maximum((if(x > y) x else y) :: ys) calls maximum (recursively) with a list obtained prepending one between x and y (depending on what the if evaluates to) to ys.