namespace r1
{
	lex r1
	{
		literal '!', 'a', 'b'
		ignore /[ \n\t]+/
	}

	def line [ '!' 'a' 'b' 'b' 'a']
}

namespace r2
{
	lex r2
	{
		literal '!'
		token id /[a-zA-Z_]+/
		ignore /[ \n\t]+/
	}

	def line [ '!' id ]
}

def item 
	[r1::line]
|	[r2::line]

def btscan 
	[item*]

P: btscan P = parse btscan( stdin )

match P ~!abb !abba !aab
print_xml(P)
print( '\n' )