CPL - Mutation - BoxC Interp

case BoxC(v) => {
     val (v1, st2) = interp(v, nv, st1)
     val newLocation = newLoc(st2)
     val newLocation2 = newLocation + 1
     val box = BoxV(newLocation2)
     val st3 = extendStore(Cell(newLocation, box), st2)

     (box, extendStore(Cell(newLocation2, v1), st3))
   }