How to recursively iterate in Scala using tuples?

Question

I am trying to populate a list of tuples however only one element is being added to the list. I have two functions. def f which generates the tuple to be added to the List of tuples (and works fine because I tested that), and def iterator which is supposed to be populating the list.

def mainFn(): List[(Int, Int, Set[Int])] = {
  def myList = List[(Int, Int, Set[Int])]()
  //t: tuple (r,c)
  def f(t:(Int,Int)): List[(Int, Int, Set[Int])] = {
    //if element is 0 add hypothesis otherwise move to next element
    if (sudoku.grid(t._1)(t._2) == 0){
      (t._1,t._2,hypothesis(t._1,t._2))::Nil
    }
    else Nil
  }

  def iterator(t:(Int,Int),li : List[(Int, Int, Set[Int])]): List[(Int, Int, Set[Int])] = {
    if (t==(0,0)) li ++ f(t)
    else if (t._2 < 9) li ++ f((t._1,t._2+1))//shifting to the element on the right
    else li ++ f((t._1+1, 0))//shifting to the next row
  }

  iterator((0,0),myList)
}

I have a Sudoku grid of the form List[List[Int]] and I want to visit each cell of the grid and if the element is 0 generate a tuple of the form (Int, Int, Set[Int]) otherwise move to the next cell. I cannot however use any looping structures, only recursive calls are permitted. I cannot figure out how to recursively call iterator so that it loops all the way through the sudoku grid.

Answer 1

I ended up using a different approach (still quite similar though):

def allHypothesis(): List[(Int, Int, Set[Int])] = {
  def myList = List[(Int, Int, Set[Int])]()
  def f(t:(Int,Int), li: List[(Int, Int, Set[Int])]) : List[(Int, Int, Set[Int])] ={
    val (row, column) = t;
    if (row == 8 && column == 9) li
    else if (column == 9) f((row+1,0),li)
    else if (sudoku.grid(row)(column)==0) f((row,column+1), li:+(row,column,hypothesis(row, column)))
    else f((row,column+1),li)
  }
  f((0,0),myList)
}