the callback function that carries out the reply action

the GrammarProd rule that we use to parse the answer

Create a simple question. 'prod' is the root GrammarProd to use for parsing the reply. 'func' is a callback function that carries out the action of the answering the question. 'func' is invoked with a single argument giving the Command object representing the answer; you can get the match tree from the Command if you need the parsed form of the answer input.

Create a Command object for a successful grammar match. 'prod' is the root match object of the grammar match. This returns a suitable Command that carries out the action of answering the question.

Parse the answer. We'll match the token list against the grammar rule. If we find a match, we'll call makeCommand() to create the command to carry out the action of answering the question.