generators.ET0LTreeGrammar("dragon curve"):
(
  { A, B },
  { F:0, +:1, -:1, conc:2 },
  {
    {
      A -> (-[A] conc +[B]),
      B -> (+[A] conc -[B])
    },
    {
      A -> F,
      B -> F
    }
  },
  A
)
