# A special token used to represent a parser or lexer error
abstract class NError
	super NToken

	# All the partially built tree during parsing (aka the node_stack)
	var error_tree = new Nodes[Node]

	# The things unexpected
	fun unexpected: String is abstract

	# The things expected (if any)
	var expected: nullable String = null

	# The error message,using `expected` and `unexpected`
	fun message: String
	do
		var exp = expected
		var res = "Unexpected {unexpected}"
		if exp != null then res += "; is acceptable instead: {exp}"
		return res
	end
end