class NameNode < TerminalNode

    def initialize(string)
	@a = string
    end

    def to_s;  @a;  end

    alias :name :to_s

    def power;  NumberNode::UNITY;  end

    def mul_eval(another)
	raise "internal error (#{name}, #{another.name})" if name != another.name
	PowNode.new(self, self.power.add_eval(another.power))
    end

    def expand(stopper) 
	raise "circular dependency for #{@a}" if stopper[@a]
	return self if basic?
	return CACHE[@a] if CACHE.include?(@a)
	CACHE[@a] = expand2(stopper)
    end

    def expand2(stopper)
	newstopper = stopper.dup
	newstopper[@a] = true
	if UDEFS.include?(@a) then
	    Units.new(UDEFS[@a]).ptree.expand(newstopper)
	else
	    p, n = UALIASES[@a]
	    u = Units.new(UDEFS[n] || n).ptree.expand(newstopper)
	    MulNode.new(u, PowNode.new(NumberNode.new(10), NumberNode.new(p)))
	end
    end

    def unalias(stopper)
	raise "circular dependency for #{@a}" if stopper[@a]
	return self unless UALIASES.include?(@a)
	p, n = UALIASES[@a]
	u = NameNode.new(n)
	q = PowNode.new(NumberNode.new(10), NumberNode.new(p))
	MulNode.new(u, q)
    end

    def foldnumber(stopper)
	return self unless UPLURALS.include?(@a)
	n = UPLURALS[@a]
	NameNode.new(n)
    end

    def basic?
	not (UDEFS.include?(@a) or UALIASES.include?(@a))
    end

    CACHE = {}

    def factor
	1
    end

end