Each instance of this type of production must define the following '->' properties in its syntax template:

actor_ is the noun phrase giving the addressee of the command, if any. A command such as TELL ACTOR TO DO X or (using the long-standing IF convention) ACTOR, DO X addresses a command to an actor; i.e., it tells the actor to carry out the command, rather than the player's avatar. A command that isn't addressed to an actor can leave actor_ as nil.

cmd_ is the *first* predicate phrase (see below), in the desired order of execution. For example, for "open the door and go north", cmd_ should be set to the match tree for the "open the door" predicate.

conj_ is any conjunction or punctuation ending the first predicate phrase. This might be a period at the end of the sentence, or a word like 'and' or 'then' that can separate multiple commands. This can be nil if there's no conjunction at all (such as when the whole command is just the first predicate). The reason we need conj_ is that it tells us where any subsequent command on the same command line starts. If cmd2_ is not nil, we'll ignore conj_ and use cmd2_ instead for this purpose.

cmd2_ is optional: it's the *second* predicate phrase. If this is not nil, it tells the parser where to start parsing the next predicate on the same command line after finishing with the first one. This is optional, even if the command line really does have more than one predicate, because the parser can use conj_ instead to infer where the second predicate must start.

(It's probably intuitively obvious what "first predicate" means, but for the sake of translators, here's a more thorough analysis. Some command productions can match more than one predicate phrase, but this is only for the sake of determining where the first one ends, syntactically. The execution engine actually only carries out the first predicate matched for a given parse tree - it simply ignores any others in the same tree. After we finish executing the first predicate from the match, we go back and re-parse the remaining text from scratch, as raw text; at that point, the next predicate in the text becomes the first predicate in the new parse tree and gets executed. We repeat this until we run out of text. So we do eventually execute everything the player types in - but not on the first parse; we have to do one parse per predicate. We have to repeat the parsing because carrying out the first action could change the game state in such a way that we'll find a different match to the next predicate than we would have if we'd parsed everything up front. By "first predicate phrase", then, we mean the one that gets executed first. The point is to carry out the user's wishes as expressed in the command, so we want the first predicate we execute to be the one that the player *intends* to be carried out first; so by "first" we really mean the one that a speaker of the natural language would expect to be performed first, given the structure of the sentence and the rules of the language. In English, this is easy: X THEN Y or X,Y or X AND Y all mean "first do X, then do Y" - the reading order is the same as the execution order.)

class CommandProduction :   Production