Maybe you can tell I spent some time with the f-troop recently.
```
scala> val size = 5
size: Int = 5

scala> val what = "strange"
what: String = strange

scala> val opt = "demystify"
opt: String = demystify

scala> val x = new Formattable {
     | def formatTo(f: Formatter,g:Int,w:Int,p:Int) =
     | { val s = if (size>1) s"there were $size $what warnings"
     |   else s"there was one $what warning"
     |   f format s }}
x: java.util.Formattable = $anon$1@5e47f5ae

scala> f"$x; re-run with $opt"
res1: String = there were 5 strange warnings; re-run with demystify
```