def generate(string)
      x = []
      @fst._generate(string) { |a| x << a.join }
      x
    end
def generate(string)
      x = []
      @fst._generate(string) { |a| x << a.join }
      x
    end
Generates a string +string+. Returns an array of generated
 strings if the string is accepted or an empty array if not.