Required return keyword - scala

Question

So I am relatively new to Scala and working through Functional Programming in Scala and just ran across something new in one of the practice problems. In hasSequences, I am required to place the return keyword in front of my return value or else nothing will return and the next line will execute. Why is this required?
def hasSubsequence[A](list: List[A], subList: List[A]) : Boolean = {
def matcher(l: List[A], sl: List[A]): List[A] = {
if (sl.isEmpty) return Nil
l match {
case Nil => Nil
case head :: tail if (head == sl.head) => head :: matcher(tail, sl.tail)
case head :: tail => matcher(tail, sl)
case _ => Nil
}
}
if (matcher(list, subList) == subList) true else false
}

Answer 1

It's required because Scala treats the return value as either the last value in the function, or a value following the return keyword. Since your example isn't the last thing in the function, how would Scala know you wanted to return it? Imagine a situation where you use a function with side effects which also has a return value. If you call the function without assigning the result to anything, there would be no way to determine if you wanted to return that value or not without these restrictions.
You could modify your function like this:
def hasSubsequence[A](list: List[A], subList: List[A]) : Boolean = {
def matcher(l: List[A], sl: List[A]): List[A] = {
if (sl.isEmpty) Nil
else l match {
case Nil => Nil
case head :: tail if (head == sl.head) => head :: matcher(tail, sl.tail)
case head :: tail => matcher(tail, sl)
case _ => Nil
}
}
if (matcher(list, subList) == subList) true else false
}
to avoid the return. Since this makes the match part of the same if statement as the return, it all becomes part of the latest statement, and you no longer need to explicitly return.