| Chapter 16: Understanding |

| 16.17. Understanding mistakes

When inspiration strikes the player, he can usually be relied upon to make a good-faith effort to communicate the new idea: he will guess the right command. If he guesses wrongly, the mistake is probably the author's, because a good author will try to anticipate all possible wordings and make all of them work.

Nevertheless it is sometimes good practice to nudge the player towards the right wording - particularly if the player has the right idea but is not explicit enough: for instance, typing TALK TO JUDGE when we really want to know what is to be said (JUDGE, GUILTY); or if the player tries something like PLAY CHESS rather than MOVE PAWN TO KING 4. Similarly, if we make a casual reference such as "In your childhood days, you loved sliding in stocking feet across this hallway", a player might type SLIDE IN STOCKING FEET: a nice idea, and which deserves a nice response, even though it asks to do something beyond the scope of the game.

Inform provides a simple mechanism for recognising a command but at the same time recognising that it does not properly specify an action. Such commands are called "mistakes", for the sake of a memorable term, but the player has not really behaved badly, and should be helped rather than reproved. For instance:

> Understand "act" as a mistake.

While that works - the command to "act" is indeed rejected - it is not very good, because no very helpful message is brought up. The following is much better:

> Understand "act" as a mistake ("To join the actors, you have to adopt a role in the play! Try PLAY HAMLET or similar.").

Or we could once again insist on a given context:

> Understand "act" as a mistake ("To join the actors, you have to adopt a role in the play! Try PLAY HAMLET or similar.") when the location is the Garden Theatre.

That still has the drawback that the command "act hamlet" will not be recognised: so the final version we want is probably

> Understand "act [text]" as a mistake ("To join the actors, you have to adopt a role in the play! Try PLAY HAMLET or similar.") when the location is the Garden Theatre.

since the "[text]" part will soak up any words the player types (or none), meaning that any command at all whose first word is "act" will be matched.

The following is often useful during beta-testing of a new work, though we would not want it in the final published edition. Many authors like to ask their testers not to try anything in particular, simply to play naturally: but to record the transcript of the session, and email it back to the author. The following command is a device to allow the tester to type a comment in to the transcript:

> Understand "! [text]" as a mistake ("Noted.").

For instance, the tester might type "! DIDN'T WE SAY DARCY WAS TALL?", to which the game would reply "Noted." - and the author can search for such comments when receiving the transcript.

If we are careful, we can make the reply depend on what was typed in the mistaken command:

> Understand "steal [something]" as a mistake ("Just TAKE [the noun] and leave without paying: that's stealing in my book.").

The care comes in because Inform applies much less checking to mistakes than to other actions, and odd errors will result if we try to refer to (say) "the second noun" in a command which did not have a second noun.

244
| Example Responding to questions starting with WHO, WHAT, etc. Catching all questions that begin with WHO, WHAT, WHERE, and similar question words, and responding with the instruction to use commands, instead.

245
| Example The Gorge at George If the player tries to TALK TO a character, suggest alternative modes of conversation.

246
| Example Hot Glass Looks Like Cold Glass Responding to references to a property that the player isn't yet allowed to mention (or when not to use "understand as a mistake").

Suppose we have a situation where the player is allowed to talk about the heat of an object only if he's properly equipped to detect it. "Hot Glass Looks Like Cold Glass" Heat is a kind of value. The heats are hot, warm, room temperature, or cold. A thing has a heat. Understand the heat property as referring to a thing when the player wears the infrared goggles. The Test Kitchen is a room. "Your own personal lab, ready for scrupulously scientific recipe research. You hope. The previous three runs of this did not go well." The pair of infrared goggles is carried by the player. The description is "A pair of head-mounted IR goggles which look very foolish when worn." The goggles are wearable. A glass dish is a kind of container. A glass dish is transparent. Three room temperature glass dishes are on the counter. Two hot glass dishes are on the counter. Two cold glass dishes are on the counter. The counter is scenery in the Test Kitchen. Instead of doing something other than examining to a hot dish: say "Ow! Crikey! You swear, and Claudia makes a sympathetic hiss. 'You're going to have a mark from that for sure,' she comments."; award -2 points. Instead of doing something when a hot dish is the second noun: say "You brush [the second noun], and wince, but manage to conceal that from Claudia."; award -1 points. Before printing the name of a dish when the player wears the goggles: say "[heat] " Before printing the plural name of a dish when the player wears the goggles: say "[heat] " So far, so good. Now, what if the player tries to GET HOT DISH when the goggles are off? "You can't see any such thing." doesn't seem like quite the right response: he can see such a thing. He just doesn't know which it is. We could go on to write a mistake rule that would scold the player for trying "get [heat] [text]" when not wearing the goggles. The problem is that this would not cover any other phrasing of the command, nor would it account for all the many other things the player might try to do with an object specified by heat. What we really want is to catch all instances of the player using the property name when not allowed to do so; and for this purpose we can borrow a trick from the chapter on Activities: After reading a command: if the player wears the goggles, make no decision; if the player's command includes "[heat]" begin; say "Without the IR goggles on, you cannot tell hot things from cold at sight."; rule succeeds; end if. Claudia is a woman in the Test Kitchen. "Your assistant Claudia stands by with [a list of things carried by Claudia]." The description of Claudia is "Infinitely patient and a very good stenographer. She is studiously avoiding giving you any sort of look that might be construed as mocking." Claudia carries a notepad, a brined chicken breast, a blowtorch, and a cup of heavy cream. Instead of asking Claudia for something which is carried by Claudia: move the second noun to the player; say "'Check, [second noun],' repeats Claudia, in the tone of one who has seen too many medical dramas. She does hand it over, though." Instead of asking Claudia for something: say "She clears her throat faintly and glances at [the second noun], as though to say that it's not hers to give." Test me with "get all / drop all / look / wear goggles / look / ask claudia for cream / put cream in hot dish / put cream in cold dish / remove goggles / get hot dish".

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