I want to create a list of `GridBagPanel.Constraints`.
I read it in the scala programming book, that there is a cool `for-yield` construction, but I probably haven't understood the way it works correctly, because my code doesn't compile. Here it is:

```
        val d = for {
            i <- 0 until 4
            j <- 0 until 4
        } yield {
            c = new Constraints
            c.gridx = j
            c.gridy = i
        }

```

I want to generate a `List[Constraints]` and for every constraint set different x,y values so later, when I later add the components, they're going to be in a grid.