Counter in for comprehension

Question

How to do Scala equivalent to this Java code:

int i = 0;
for(String x: xs) {
    for(String y : ys) {
        foo(x, y, i);
        i+=10;
    }
}

Answer 1

There are multiple ways of doing it:

var i = 0                                 
for(x <- xs;y <- ys) {
  foo(x,y,i)
  i = (i+10)
}

To do it functionally without using external i:

xs.foldLeft(0){(a:Int,b) =>
   ys.foldLeft(a){(c:Int, p) =>
     foo(b,p,a)
     c+10
   }
}