public int defineChannelName(String name) {
		Integer prev = channelNameToValueMap.get(name);
		if (prev == null) {
			return defineChannelName(name, getNewChannelNumber());
		}

		return prev;
	}
Define a token channel with a specified name.

<p>
If a channel with the specified name already exists, the previously
assigned channel value is returned.</p>

@param name The channel name.
@return The constant channel value assigned to the channel.
tool/src/org/antlr/v4/tool/Grammar.java