lex start
{
	ignore /[ \t\n]+/
	token id /[a-z0-9]+/
	literal ',', '.', '*', '(', ')'
}

def bigger ['(' item* ')']

def item [id] | [bigger]

def lang [item*]

B: bigger = construct bigger "( b1 b2 )"
print( construct lang "a [B] c" '\n' )