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§17.3. Overriding existing commands
Suppose we are devising specialist commands for a game of whist, and we want "discard" as one of them. Looking at the table of commands in the Action index, we find that, inconveniently enough, "discard" already has a meaning: it is synonymous with "drop", and while that might be sensible most of the time, it is perfectly wrong now. We need a way to free up "discard" for our own use. We can do that by:
Understand the command "discard" as something new.
This cuts it loose, so to speak, and ready to be given new meanings. If we check the Actions index again, we find no mention of "discard" - it is now a blank slate - but "drop" is still exactly as it was. We could now say something like:
Understand "discard [something]" as discarding.
(If we had declared that "drop" was something new, the whole thing would have happened in reverse, with "discard" retaining all of the original grammar. Inform does not distinguish between a command and its synonym.)
The "... as something new" sentence works even for a command which did not exist anyway, for instance with:
Understand the command "zylqix" as something new.
Of course this does nothing - but it is intentional that it generates no problem messages: it means that the sentence can be used to force a command to be fresh and untouched by previous definitions, which might be useful when working with extensions by other people.
It is also possible to clear out all the commands leading to a given action:
Understand nothing as taking.
The commands "take" and "get" will still exist, but now they'll only have their other senses (for taking off clothes, for getting out of boxes).
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The Trouble with Printing
Understand the command "read" as something new. Understand "read [something]" as reading. Reading is an action applying to one thing, requiring light. Check reading: if the printing of the noun is "blank", say "Nothing is written on [the noun]." instead. Carry out reading: say "You read: [printing of the noun][line break]". Report reading: do nothing.
Berkeley's report is a thing in the Archive. The description is "A report from Governor Sir William Berkeley of Virginia, in 1671, in answer to the queries sent by the Commissioners of Plantations the year previous. Of this report the better part is burned and only a tail fragment remains." The printing of Berkeley's report is "I thank God, [italic type]there are no free schools[roman type] nor [italic type]printing[roman type], and I hope we shall not have these hundred years; for [italic type]learning[roman type] has brought disobedience, and heresy, and sects into the world, and [italic type]printing[roman type] has divulged them..."
Since we defined reading as an action requiring light, we could further distinguish reading and examining (if we wanted) by writing some different visibility rules for it.
Back in the chapter on randomization, we explored a way to create a randomized combat system. That system didn't allow for multiple weapons, though. Here we explore how to create an ATTACK IT WITH action that will let the player choose between weapons with different maximum powers.
We're also going to rewrite that original "instead of attacking:" rule into an attacking it with action that can be performed equally by the player or by any of the player's enemies.
The Arena is a room. "Sand, blood, iron. These festivals are normally held on hot days, but the sun has gone behind a cloud and fat drops of rain now and then spatter the arena floor." The gladiator is a man in the Arena. "A bare-chested Scythian gladiator faces you, wielding [a list of weapons carried by the gladiator]."
In our simpler version of this example we set the current hit points by hand, but in a game with many characters this would get dull and repetitive, so here we'll use a "when play begins" to set all current hit point values automatically to maximum:
Carry out diagnosing:
say "[if the noun is the player]You have[otherwise][The noun] has[end if] [current hit points of the noun] out of a possible [maximum hit points of the noun] hit points remaining."
In our new system, we want to specify what is being used for an attack. This means that we need to create a new "attacking it with" action, and also that we should disable the existing "attacking..." command.
Here's why: If we leave the default attack command in place, Inform will continue to accept commands like >ATTACK GLADIATOR, but reply foolishly with the default "Violence is not the answer..." response.
A somewhat better approach would be to change the reply of >ATTACK GLADIATOR to say something like "You must specify a weapon to attack with." But this is still less than ideal, because it means that the player has to then rewrite his entire command. If, on the other hand, we take out "ATTACK GLADIATOR" entirely, the game will always prompt "What do you want to attack the gladiator with?" -- which teaches the player the correct command structure for this particular game, and avoids pretending to understand any command that is not meaningful within this game.
This is a little bit of work because ATTACK has a lot of synonyms in the default library, but if we look through the actions index we can find them all:
Now we make our new command:
Note that we've specified "one carried thing", because we want the player to pick up a weapon to use if necessary. And now we assign all the old attack vocabulary to apply to the new command:
This may seem counter-intuitive, but order of source code matters here: we first get rid of the old, default vocabulary, then define our new action, then make the vocabulary apply to that new action. Inform will now understand >HIT GLADIATOR WITH TRIDENT, >BREAK GLADIATOR WITH TRIDENT, and so on.
Our new action is also a perfect place to use an action variable: we're going to need to choose an amount of damage done and refer to that several times in our action rules. So let's set that up first:
Setting action variables for attacking something with something:
if the second noun is a weapon:
let the maximum attack be the maximum damage of the second noun;
now the damage inflicted is a random number between 1 and the maximum attack.
Check an actor attacking something with something (this is the can't attack with something that isn't a weapon rule):
if the second noun is not a weapon:
if the actor is the player, say "[The second noun] does not qualify as a weapon.";
stop the action.
Check an actor attacking something with something (this is the can't attack a non-person rule):
if the noun is not a person:
if the actor is the player, say "[The noun] has no life to lose.";
stop the action.
Carry out an actor attacking something with something (this is the standard attacking it with a weapon rule):
decrease the current hit points of the noun by the damage inflicted;
if the noun is dead and the noun is not the player:
now the noun is nowhere.
Though our checks and carry-out rules are similar regardless of who is acting, we're going to want actions to be described differently for different actors, so we'll use separate "report attacking" and "report someone attacking" rules. We'll also make some special cases for when the character has died as a result of the attack:
Report someone attacking the player with something when the player is dead (this is the player's-death priority rule):
say "[The actor] attacks you with [the second noun], finishing you off!";
end the story;
stop the action
Report someone attacking the player with something (this is the standard report someone attacking the player with rule):
say "[The actor] attacks you with [the second noun], causing [damage inflicted] point[s] of damage!" instead.
Report someone attacking something with something (this is the standard report attacking it with rule):
say "[The actor] attacks [the noun] with [the second noun], causing [damage inflicted] point[s] of damage!" instead.
Those devoted to role-playing will note that our form of randomization is still pretty naive: most RPG systems use multiple dice in order to create more interesting probability curves. For a system that simulates actual dice-rolling, see the full "Reliques of Tolti-Aph" game.