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Chapter 17: Understanding
§17.1. Understand; §17.2. New commands for old grammar; §17.3. Overriding existing commands; §17.4. Standard tokens of grammar; §17.5. The text token; §17.6. Actions applying to kinds of value; §17.7. Understanding any, understanding rooms; §17.8. Understanding names; §17.9. Understanding kinds of value; §17.10. Commands consisting only of nouns; §17.11. Understanding values; §17.12. This/that; §17.13. New tokens; §17.14. Tokens can produce values; §17.15. Understanding things by their properties; §17.16. Understanding things by their relations; §17.17. Context: understanding when; §17.18. Changing the meaning of pronouns; §17.19. Does the player mean...; §17.20. Multiple action processing; §17.21. Understanding mistakes; §17.22. Precedence
|Contents of Writing with Inform|
|Chapter 16: Tables|
|Chapter 18: Activities|
|Indexes of the examples|
During play, the computer and the player alternate in writing messages to each other: in the player's case, these are short instructions, usually saying what to do next. A wide range of such "commands" are automatically understood, but these only apply to the standard built-in actions. (This wide range is conveniently tabulated in the Commands part of the Actions index.) If we want the player to be able to command new actions, then we need to specify what is to be understood as what. For this, we supply special sentences starting with the word "Understand".
Suppose we return to the earlier example of a newly created action:
Photographing is an action applying to one visible thing and requiring light.
We then supply lines of grammar (as they are called) for Inform to recognise, like so:
Understand "photograph [someone]" as photographing.
Understand "photograph [an open door]" as photographing.
As usual, the square brackets indicate something which stands for text, rather than text to be taken verbatim. "[someone]" needs to be the name of anything of the kind "person", for instance (though as usual that person will need to be in sight of the player for the name to be accepted). The first word - in these examples "photograph" - must be something definite, not a substitution like this.
For obvious reasons, this pattern of words needs to match the expectations of the action. Photographing applies to "one visible thing" - the "visible" just means it does not need to be touched, only seen - so neither of these would be allowable:
Understand "photograph" as photographing.
Understand "photograph [someone] standing next to [something]" as photographing.
The first is probably bad because it supplies no things at all, the second is certainly because it supplies two: what we want, of course, is just the one. (The reason the first is only probably bad is that it's possible to tell Inform how to choose the object if the player doesn't: see the "supplying a missing noun" activity.)
|Start of Chapter 17: Understanding|
|Back to Chapter 16: Tables: §16.19. Table amendments|
|Onward to §17.2. New commands for old grammar|
In Mayan culture, colours seem to have been used as names for the primary directions: for instance, "red" implies east as the colour of sunrise. So the following might be a stylish touch for a game in which the player has to get inside the Mayan world-view:
Understand "white" and "sac" as north. Understand "red" and "chac" as east. Understand "yellow" and "kan" as south. Understand "black" and "chikin" as west.
We could also use a colour as a verb:
And now a few extra rooms to try it out in:
The Square Chamber is a room. "A sunken, gloomy stone chamber, ten yards across. A shaft of sunlight cuts in from the steps above, giving the chamber a diffuse light, but in the shadows low lintelled doorways to east and south lead into the deeper darkness of the Temple."
The Wormcast is east of the Square Chamber. The Corridor is south of the Square Chamber.
We have seen before how to define a new action from scratch, but we may want to review here, using a simple command that requires no objects.
Understand "xyzzy" or "say xyzzy" or "cast xyzzy" as casting xyzzy.
Check casting xyzzy:
if the player does not wear the amulet of elocution, say "You are unable to articulate the second 'z' separately from the first, and the spell fails in a disdainful puff. Must be Parisian magic." instead;
if the player has the plate, say "The plate of cheeses twitches uncomfortably, aware that it should be doing something, but not sure what." instead.
Report casting xyzzy:
say "Under the influence of the Amulet of Elocution, you pronounce this as Xhi-zee. And lo, from nowhere, a [plate] appears!"
The amulet of elocution is a wearable thing. It is carried by the player. The description is "A heavy gold ring on a chain. If heated in an ordinary house fire, it glows with the words, 'Moses Supposes His Toeses Are Roses.'"
The plate is a portable supporter. On the plate is a very ripe ooze. Instead of smelling the ooze, say "It smells like socks. This is going to be wonderful." The ooze is edible. The printed name of the plate is "plate[if the plate supports the ooze] of cheese[end if]". The description of the ooze is "Definitely genuinely cheese." Understand "cheese" as the ooze.
Instead of eating the ooze: now the ooze is nowhere; say "You are transported..."; move the player to Paradise.
The Cheez Factory is a room. "All around you are squares of pressed orange polymer, or possibly cheez. Your only hope is the magic word your uncle taught you: XYZZY." The squares of pressed orange polymer are scenery in the Factory. The description is "You see nothing special about the squares of pressed orange polymer. Nothing special at all." Understand "square" or "cheez" as the squares.
Paradise is a room. The description is "Well, it might just be one of the posh upper rings of purgatory, if you're entirely honest with yourself."
Test me with "x squares / x amulet / x cheese / xyzzy / wear amulet / xyzzy / x ooze / smell ooze / eat ooze".
XYZZY is a magic word from the original Adventure, and many other games respond to it with some sort of amusing message.
If we wanted to define a brand new verb that did affect a specific object, we might begin like this:
Understand "hydrolyze [something]" as hydrolyzing. Hydrolyzing is an action applying to one thing.
Carry out hydrolyzing:
say "[The noun] cannot be hydrolyzed."
Instead of hydrolyzing the xylan:
move the xylose to the holder of the xylan;
now the xylan is nowhere;
say "At once the xylan becomes xylose."
There is a xylose sample. The xylan sample is a thing in Plant Cell Wall. The description of the xylan is "A polysaccharide. Totally useless. If only you had some xylose, instead!" The description of the xylose is "Awesome!"
Of course, how our players will ever solve this problem is another question (especially if their biology and chemistry are both rusty). When adding entirely new commands to a game, it is often a good idea to provide as many ways of phrasing the command as possible; to drop hints about the correct phrasing within the game's text; or even to tell the player about the expanded command list in some documentation or help at the beginning of the game. So for instance we might also add
Understand "break down [something] with water" or "break [something] down with water" as hydrolyzing.
And these lines will also provide syntax for our new command, without interfering with the previous syntax. It's also good to anticipate alternative (British or American) spellings. People's typing habits are hard to overcome, even if they know you are spelling the word the other way. It is probably best not to annoy them unduly. So:
Then some text in-game might offer a clue, subtle or (since this is an example) blunt:
Instead of examining the player, say "You're a drop of water, which means that you can break down certain chemicals!"
Understand "break down [something]" or "break [something] down" as hydrolyzing.
And finally, we could try adding instructions explicitly:
Understand "help" or "hint" or "hints" or "instructions" or "info" or "about" as asking for help. Asking for help is an action out of world. Carry out asking for help: say "The following commands are understood, in addition to the standard ones: EVAPORATE, FREEZE, HYDROLYZE, SUBLIME..."
...though of course in fact these other commands won't be available until we define them, too.
This last approach, defining all the extra commands up front, is especially useful if these commands are very technical or unusual; if they are needed early in the game, before you've a chance to educate the player; or if they are not suggested by any in-game objects. A player who encounters a tool with an obvious use, such as a hairbrush, will likely think of trying to BRUSH things with it. It's harder to rely on his guessing actions that are both outside the range of usual commands and unrelated to any of the visible props, however.