# Produce a graphiz file for the syntaxtic tree rooted at `self`.
	fun to_dot(filepath: String)
	do
		var f = new FileWriter.open(filepath)
		f.write("digraph g \{\n")
		f.write("rankdir=BT;\n")

		var a = new Array[NToken]
		to_dot_visitor(f, a)

		f.write("\{ rank=same\n")
		var first = true
		for n in a do
			if first then
				first = false
			else
				f.write("->")
			end
			f.write("n{n.object_id}")
		end
		f.write("[style=invis];\n")
		f.write("\}\n")

		f.write("\}\n")
		f.close
	end