9. Props: Food, Clothing, Money, Toys, Books, Electronics

Inform provides an either/or property called "edible" and an action, "eating", for consuming edible things:

For eating something not immediately to hand, see Lollipop Guild ★★★. Delicious, Delicious Rocks ★★★, conversely, adds a sanity check which prevents the player from automatically taking inedible things only to be told they can't be eaten.

Inform does not normally simulate taste or digestion, but to provide foods with a range of flavours, see Would you…? ★; to make eating different foods affect the player differently, see Stone ★, or for the extreme case of poisoning foods, Candy ★. In MRE ★, hunger causes the player problems unless he regularly finds and eats food.

The kind "container" allows one thing to contain others. Things are sometimes containers automatically, sometimes by instruction:

The matchbox, like the bucket, is a container. Containers come in all sizes and have a variety of behaviours, mainly controlled by the properties we give them: they can be "open" or "closed", "opaque" or "transparent" (when closed), "openable" or not, "lockable" or not, "enterable" or not. The basic ideas of containment are to do with carrying and sometimes hiding the contents, and Inform makes this easy. Allowing for locking and unlocking is again straightforward:

Two built-in extensions enhance and modify the behavior of locks and keys: Locksmith automates a number of steps, automatically unlocking doors when trying to open them (for instance). Skeleton Keys allows us to define multiple keys that unlock the same object, rather than being restricted to one matching key per item.

For a container with a combination lock, rather than a key, see Safety ★; for a more sophisticated safe requiring digits dialed over multiple turns, see Eyes, Fingers, Toes ★.

Trachypachidae Maturin 1803 ★★ provides a bottle that is stoppered with a cork: when it is closed, the cork is part of the bottle, but otherwise the cork becomes a separate object we can carry around.

The normal assumption is that there is no problem with any two portable items being carried together, but in reality they may affect each other. (For effects like magnetism, or getting each other wet, or setting each other on fire, see the Physics chapter.) Here is a cat which, if boxed up with one or more items of food, will eat something each turn until all is gone:

The examples below provide subtler effects, adapting text to the current situation. In Cinco ★, the container's name changes depending on what it contains: putting beef in a taco allows the player to call it a SHREDDED BEEF TACO. In Unpeeled ★ and Shipping Trunk ★, the description of something inside a container changes according to other things are alongside it. This is taken further in Hudsucker Industries ★★, which describes the contents of a container as a group.

Finally, any action that destroys a container has to consider what to do with the things inside. Fallout Enclosure ★★★ demonstrates a zapping action that destroys cash registers and shelves but leaves their contents tidily behind.

A person can wear any (portable) thing which has the "wearable" property. (This property seldom needs to be quoted because it is deduced automatically from sentences like "Trevor wears a red hat.")

In most traditional IF, clothing is only used when it is exceptional in some way. That is, we ignore the three to eight different garments most people are wearing at any given time - the everyday clothes which people wear without thinking about them - and only simulate the unexpected extras: a borrowed jaunty red hat, a radiation-proof space suit, and so on.

These unusual garments turn up only occasionally in play and usually one at a time, so Inform does not normally provide rules to restrict how much or little is worn, or in what unlikely combinations. Get Me to the Church on Time ★★★ categorises clothing by body area (trousers for lower body, shirts for upper); Bogart ★★★ by layer, distinguishing underwear from outer garments. What Not To Wear ★★ combines both into a general-purpose system adequate for most kinds of clothing situations.

Hays Code ★ is a somewhat stripped down version.

Clothes are normally single things which have no function other than display and concealment, but Being Prepared ★ gives them pockets which act as containers, and Some Assembly Required ★ allows clothes to be stitched together from pieces of cloth.

Money could be anything which the two people in a bargain both agree is valuable. Here, the player and an ogre agree on a copper coin as money:

Now Inform does provide an action, "buying", and a command for it, BUY, but they ordinarily respond simply "Nothing is on sale." This is no longer true, so we should make BUY CAKE work. The difficulty here is that a command like BUY CAKE does not specify what should be handed over in exchange. Here we just check that the player has the coin, but in principle we could check for any of a range of monetary tokens - coins, notes, cheque book, debit card, and so on.

In more advanced economies, where shopping replaces barter, the seller will stock a wide range of differently priced goods. For a tabulated catalogue of wares, see Introduction to Juggling ★★★: to allow the player to negotiate prices, see Money for Nothing ★★. In both of those examples, the player's current financial worth is simulated only as a current total amount of money carried - say, $2.50. This is typical, because in most situations what matters is how much money is in the pocket, not how it is made up. Money behaves more like a liquid than a set of items: hence terms like "liquidity", "cash flow" or Frozen Assets ★ - the name of the simplest example demonstrating this. If we really need a comprehensive simulation down to pieces of currency - where it makes a difference carrying four quarters rather than a dollar bill, because the quarters can be fed into a vending machine - see Nickel and Dimed ★★★.

Fabrication ★★ takes the problem in a different direction, making calculations about the cost of a new garment based on the price of the pattern, the quantity of fabric required, and the value of the fabric type chosen -- showing off what we can do with unit multiplication in Inform.

Widget Enterprises ★ explores the challenge of pricing widgets for maximum profit, given certain necessary costs and customers with varying willingness to pay.

Most toys are single things, and no harder to create than any other small items, but games often require a multitude of tokens to be combined, and this can be logistically tricky.

The classic example is a pack of playing cards, where the player must individually control 52 items but without fussy commands or verbose text being printed back. Jokers Wild ★★ provides a simple "one card at a time" approach; Tilt ★★★ is more sophisticated, with 52 independently accessible cards; Tilt 2 ★★★ can further judge the value of a selection of cards - the ranking of a poker hand.

Drawing cards from a shuffled pack is only one source of randomness. Games of chance also involve items drawn from a bag: Wonka's Revenge ★ provides just such a lottery. More often, dice are thrown. A single die is easy enough:

Quick, but not very good. Most dice games involve rolling more than one die at a time, to get a more interesting distribution of outcomes: they may also involve special rules applying to doubles, for instance. See Do Pass Go ★.

Many things can be read, from warning notices to encyclopaedias, and a range of techniques is needed to provide them because the quantity of text, and how it presents itself, can vary so much. With a small amount of very large type, the player should not need any command at all to read the text:

If the print is smaller, or the object portable, the player will expect to use the EXAMINE command:

But if the object is a leaflet, say, EXAMINE should only describe the cover: READ would be the command a player would expect to use to get at the text itself. Inform normally defines READ to be the same command as EXAMINE, which is good for things like the business card, but counter-productive here. The Trouble with Printing ★ shows how to separate these two commands, allowing any thing to have a property called its "printing" for text produced by READ, which will be different from its "description", the text produced by EXAMINE.

If the object is a lengthy diary, say, nobody would read it from cover to cover in a single IF turn. We might then want to allow the player to turn the pages one by one, with commands like READ PAGE 4 IN DIARY or READ THE NEXT PAGE: see Pages ★.

If the object is an encyclopaedic reference work, the player would consult named entries: see Costa Rican Ornithology ★★★, which allows commands like LOOK UP QUETZAL IN GUIDE.

Still larger sources of text often occur in IF: libraries or bookshelves, where many books are found together, and it is clumsy to write them as many individual items. One approach is to simulate an entire bookshelf with a single thing: see Bibliophilia ★★. (This is much like looking up topics in a single book, except that each topic is a book in itself.) Another is to provide each book as an individual item, but have them automatically join together into a single portable collection: see AARP-Gnosis ★★.

Signs, leaflets and encyclopaedias, being printed, have a wording which will never change during play. But sometimes the player reads something which acts of its own accord. Text substitutions are usually all that is needed to achieve this:

This is easy because we know all the variations we want. But what if we want the player to write his own text, for instance, adding to a diary? This is trickier, because it means storing text as the player typed it, and replaying it later. (And suppose the player types reams and reams of text, not just a few words as we might have hoped?) The Fourth Body ★ and The Fifth Body ★★ show how to use an external file - a multimedia trick requiring features only available if the project is set to the Glulx story file format - to handle even the most difficult cases.

Should we want a computer that responds to vocal commands, as in ASK COMPUTER ABOUT KLINGONS, the built-in extension Inanimate Listeners will allow the player to talk to inanimate objects as well as people.

Writing on something is only one way a player can change its visual appearance. IF authors have long been wary of paint brushes, because a sufficiently motivated player could go through a whole landscape like a graffiti artist with a railway bridge. We want to give the player the illusion of freedom of action, while avoiding a situation where unlimited numbers of different decorations might be needed - that would need a table of potentially unlimited size.

One approach is to limit the number of items which can be decorated. In Palette ★, only the canvas can be painted, and each image overlays the last. Early Childhood ★★★ increases the range to allow a whole kind ("block") to be painted, and also shows how the changing colours can be used to distinguish between otherwise identical objects.

Brown ★★★ finds a different way to limit the number of simultaneous decorations: almost anything can have a red sticky label attached, but there is only one red sticky label. (So to decorate a new item, the player must first un-decorate an old one.)

The "device" kind provides for the simplest form of machine: one which is, at any given moment, switched on or switched off. Inform looks after this state, but leaves it to us to make the machine actually do something:

One primary dictionary definition for a machine is "an apparatus using or applying mechanical power and having several parts", and we often use the "part of" relationship to build machinery. Control Center ★ provides a neat way to display the component parts of a machine to the player who examines it.

One component almost always part of an electrical machine is the (literal) switch, lever or button to control whether it is switched on or off. In Model Shop ★★ just such an on/off button is automatically made part of every device.

While an electrical device has only two states, a mechanical machine might have many, and for these the best approach is to define a kind of value naming the possibilities: see Signs and Portents ★★★, where the states are the possible destinations pointed towards.

Perhaps stretching the definition of "machine", What Makes You Tick ★ demonstrates a fishing pole which the player can put together from several pieces.

IF authors often provide clues or background information to the player by means of radio broadcasts, TV shows or video tapes because they can talk to the player without needing to listen back, or to react to what the player does. The simplest radio set, like the one in Aftershock ★★★, really only has one thing to say: which is serendipitously being broadcast just at the moment the player tunes in (regardless of when that is). The next simplest approach is to spool a broadcast on an endless loop taking several turns to play through, as in Radio Daze ★.

Televisions come in all shapes and sizes, and Aspect ★ allows their shape ("aspect ratio") to be described by the player.

In Channel ★★, we can also refer to the television by what it is currently showing: thus WATCH CHANNEL 4 will work if the set is indeed tuned to 4. In Channel 2 ★★★, numbered channel changing is taken further: we can now TUNE TV TO CHANNEL 3, as well. Channel 2 ★★★ is a reasonable base implementation of a television for many purposes.

Telephones are much harder to achieve than televisions and in some ways as difficult to make convincing as a human character is - though of course there are corners which can be cut: we could have the reception drop off, or the other party hang up in a misunderstanding, and so on.

A single telephone line is tricky enough to provide that one might just as well have a general solution providing a whole network. Four Cheeses ★★★ demonstrates a system where we can dial either people or numbers: CALL JANET ON TELEPHONE, or CALL 7103, for instance.

While Four Cheeses ★★★ provides only four-digit phone numbers, like internal company extensions, Alias ★★★ shows how to manage US-style seven digit numbers.

Finally, we might occasionally want the player to be able to address a microphone or telephone receiver directly when the identity of the person on the other end is unknown, in the form TELL MICROPHONE ABOUT CRIME. Ordinarily Inform will disallow this because we're not allowed to talk to inanimate objects, but the extension Inanimate Listeners provides more options.

The simplest form of clock is a wrist watch. Here is a choice of analogue or digital:

Better clocks would allow us also to set the time, and to stop and start them: see Tom's Midnight Garden ★.

Scientific instruments provide sharper versions of our own senses. In the case of vision, they allow us to see closer up, or further away. It's a convention of IF that people can normally see only the current location, that is, they cannot see from one location into another. The boundary of the current room is like a horizon, even out of doors (though it's true that there are ways to disguise that with a continuous outdoor landscape). Ginger Beer ★★ provides a telescope able to see into other rooms.

Witnessed 2 ★ provides a meter which measures how close a ghost is to the player.

Recording what is going on, for later playing back or examination, is difficult because the range of situations is very complex. Exactly how much information should we store when we make a recording, and will this require problematically large tables? Will it be difficult even to do at all?

The usual approach is to record only basic details of events or situations. In If It Hadn't Been For… ★ the tape recorder preserves only a few different sounds - footsteps, creaking, rustling - rather than capturing exactly the sound of every action taking place in earshot. In Claims Adjustment ★★, we can take up to 36 Polaroid-style photographs, but each is described only by saying what it is a photo of. Thus we can have a photograph of a vase, or even a photograph of a photograph of a vase (because that too is a thing), but not a photograph of a still life in which several items have been gathered together by the player. That would ordinarily require too much storage.

A similar trick, though involving impromptu sculpture rather than photography, can be found in Originals ★. (The artist magically "manifests" these models rather than sculpting the conventional way in order to avoid the nuisance of carrying around raw materials - wax maquettes and so forth - which would clutter up the example.)

Text, of course, can store arbitrary descriptions. Mirror, Mirror ★ provides a perfect visual recorder: it remembers a room description exactly as the player saw it at the time.

Actor's Studio ★★ provides a video camera that records and time stamps all actions performed in its presence while it is set to record.