# If `re` matches at current index in the input, advance index and return the match
	# Else return null.
	private fun match(re: Pattern): nullable String do
		if index >= input.length then return null
		var match = input.search_from(re, index)
		if match != null then
			index = match.after
			column = match.after
			return match.to_s
		end
		return null
	end