Inform 7 Home Page / Documentation

§2.2. Varying What Is Read

Making the printed text adapt to circumstances only makes half of the conversation graceful: the other half is to allow the player's commands to have a similar freedom. The things the player can refer to should always respond to the names which would seem natural to the player. Inform provides a variety of techniques for understanding words always, or only under certain conditions; and, if need be, we can also get direct access to what the player has typed in order to examine it with regular expressions. (This last resort is rarely necessary.)

First Name Basis shows how to assign names to things or to kinds of thing - if, for instance, we want the player to be able to refer to any man as "man" or "gentleman":

Understand "man" or "gentleman" as a man.

We may also sometimes want to give names that are specifically plural, as in

A duck is a kind of animal. Understand "birds" as the plural of duck.


Understand "birds" as the plural of the magpie.

Vouvray demonstrates.

A common challenge arises when two objects have names that overlap or are related, and we wish Inform to choose sensibly between them: for instance, a cigarette vs. a cigarette case. If a word should apply to something only as part of a phrase (e.g., "cigarette" alone should never refer to the cigarette case) we can manage the situation as follows:

The case is a closed openable container. The printed name is "cigarette case". Understand "cigarette case" as the case.

Because "cigarette" here appears only as part of the phrase "cigarette case", it will be understood only in that context; the conflict with the bare cigarette will not arise.

As a variant, we may want one object only to take precedence over another in naming. If we wanted the player to be allowed to refer casually to the cigarette case as "cigarette" when (and only when) the cigarette itself is not in view, we could add

Understand "cigarette" as the case when the cigarette is not visible.

Tricks which consider the visibility of other objects can be bad for performance if used widely; but for adding finesse to the treatment of a few items, they work very well.

(There may still arise cases where the player uses a name which can legitimately refer to two different things in view. To deal with this situation, we may want the Does the player mean... rules, explained in the chapter on Understanding; and to change the way the story asks for clarification, see the two activities Asking which do you mean and Clarifying the parser's choice of something.)

Names of things which contain prepositions can also be tricky because Inform misreads the sentences creating them: Laura shows how some awkward cases can be safely overcome.

A more difficult case is to ensure that if we change the description or nature of something in play, then the names we understand for it adapt, too. "Understand... when..." can be all that's needed:

Understand "king" as Aragorn when we have crowned Aragorn.

Or, similarly, if we want some combination of categories and characteristics to be recognized:

Understand "giant" as a man when the item described is tall.

"The item described" here refers to the thing being named. "...when" can even be useful in defining new commands, and Quiz Show demonstrates how to ask open-ended questions that the player can answer only on the subsequent turn.

Properties can also be matched without fuss:

Tint is a kind of value. The tints are green, aquamarine and darkish purple. The wallpaper is fixed in place in the Hotel. The wallpaper has a tint. Understand the tint property as describing the wallpaper.

This allows EXAMINE AQUAMARINE WALLPAPER if, but only if, it happens to be aquamarine at the moment. Relationships can also be matched automatically:

A box is a kind of container. The red box is a box in the Toyshop. Some crayons are in the red box. Understand "box of [something related by containment]" as a box.

which recognises BOX OF CRAYONS until they are removed, when it reverts to plain BOX only.

Greater difficulty arises if, using some variable or property or table to mark that a bottle contains wine, we print messages calling it "bottle of wine". We are then honour-bound to understand commands like TAKE BOTTLE OF WINE in return, not to insist on TAKE BOTTLE. Almost all "simulation" IF runs in to issues like this, and there is no general solution because simulations are so varied.

A converse challenge arises when we want to avoid understanding the player's references to an object under some or all circumstances. This is relatively uncommon, but does sometimes occur. For this situation, Inform provides the "privately-named" property, as in

The unrecognizable object is a privately-named thing in the Kitchen.

Here "privately-named" tells Inform not to understand the object's source name automatically. It is then up to us to create any understand lines we want to refer to the object, as in

Understand "oyster fork" as the unrecognizable object when the etiquette book is read.

Of course, if we need an object that the player is never allowed to refer to at all, we can just make this privately-named and then not provide any understand lines at all.

A final source of difficulty is that by default Inform truncates words to nine letters before attempting to identify them. This is no problem in most circumstances and is likely to go unnoticed -- until we have two very long words whose names are nearly identical, such as "north-northwest exit" and "north-northeast exit". (To make matters worse, a punctuation mark such as a hyphen counts as two letters on its own.)

When we are compiling for Glulx, the limit is easily changed with a single line, setting the constant called DICT_WORD_SIZE. For instance, if we wanted to raise the limit to 15, we would write


When compiling for the Z-machine, the solution is harder. North by Northwest shows how to use the reading a command activity to pre-process very long names, rendering them accessible to the parser again.

Inform also allows the player to refer to the most recently seen objects and people as IT, HIM, HER, and so on. It sets these pronouns by default, but there are times when we wish to override the way it does that. Pot of Petunias shows off a way to make Inform recognize an object as IT when it would not otherwise have done so.

* See Liquids for a resolution of this bottle-of-wine issue

* See Using the Player's Input for an example (Mr. Burns' Repast) in which a fish can be called by any arbitrary word as long as it ends in the letters -fish

* See Memory and Knowledge for a way to refer to characters whom the player knows about but who aren't currently in the room

* See Clarification and Correction for ways to improve guesses about what the player means

* See Alternatives To Standard Parsing for several esoteric variations on the default behavior, such as accepting adverbs anywhere in the command, and scanning the player's input for keywords

arrow-up.png Start of Chapter 2: Adaptive Prose
arrow-left.png Back to §2.1. Varying What Is Written
arrow-right.png Onward to §2.3. Using the Player's Input

*ExampleFirst Name Basis
Allowing the player to use different synonyms to refer to something.

*ExampleQuiz Show
In this example by Mike Tarbert, the player can occasionally be quizzed on random data from a table; the potential answers will only be understood if a question has just been asked.

*ExamplePot of Petunias
Responding sensibly to a pot of petunias falling from the sky.

Some general advice about creating objects with unusual or awkward names, and a discussion of the use of printed names.

Adding synonyms to an entire kind of thing.

**ExampleNorth by Northwest
Creating additional compass directions between those that already exist (for instance, NNW) -- and dealing with an awkwardness that arises when the player tries to type "north-northwest". The example demonstrates a way around the nine-character limit on parsed words.