-------------------------------------------------------------------------------
--         Give unique names to rules
-------------------------------------------------------------------------------
ATTR Nonterminal Nonterminals
     Production Productions
     Rule Rules  [ | rulenumber : Int | ]

SEM  Grammar
  |  Grammar nonts.rulenumber = 0

SEM  Rule
  |  Rule lhs.rulenumber = @lhs.rulenumber + 1
          loc.rulename   = maybe (identifier $ "rule" ++ show @lhs.rulenumber) id @mbName