4.14. Assemblies and body parts

| Chapter 4: Kinds |

| 4.14. Assemblies and body parts

In the previous chapter, we saw that it was possible to make sub-parts of things. For instance,

> The white door is in the Drawing Room. The handle is part of the white door.

creates a door with an attached handle. But what if we want to say that not just this door, but every door, should have a handle? To do this we first need to create a kind called "handle", since there will clearly need to be many handles. The solution is:

> A handle is a kind of thing. A handle is part of every door.

"Every" is a loaded word and best used sparingly. A sentence like "A handle is part of every handle" would, if taken literally, mean that a handle takes forever to make and is never finished. Inform will reject this, but the moral is clear: we should think about what we are doing with "every".

We will usually want to work with smaller collections - not literally every room, but with a whole set of them all the same. We can do that like so:

> A silver coin is a kind of thing. A banking room is a kind of room. Five silver coins are in every banking room.

The effect of sentences like these is to make what we might call "assemblies" instead of single things. When a banking room is created, so are five more silver coins; when a door is created, so is another handle. Such sentences act not only on items created later on in the source text, but also on all those created so far.

This is especially useful for body parts. If we would like to explore Voltaire's suggestion that history would have been very different if only Cleopatra's nose had been shorter, we will need noses:

> A nose is a kind of thing. A nose is part of every person.

Of course, if we make an assembly like this then we had better remember that the player is also a person and also gets a nose. In fact slightly odd things can happen if we combine this with changing the identity of the player. This works:

> Cleopatra is a woman in Alexandria. The player is Cleopatra.
> A nose is a kind of thing. A nose is part of every person.

but if those lines are in reverse order then Cleopatra's nose is assembled before she becomes the player, with the result that it ends up called "Cleopatra's nose" rather than "your nose" in play - which is very regal but probably not what we want. To avoid this, settle the player's identity early on in the source text.

All of the assemblies above make objects. Most make these new objects "part of" existing ones, but as we saw, they can also be "in" or "on" them. In fact, though, assemblies work in much more general ways: they can assemble values of almost any kind, placed in almost any relationship. To make use of that, we need to create a new verb, a topic which won't be covered properly until a later chapter, but here goes:

> A colour is a kind of value. The colours are red, green and blue.

> Liking relates various people to various colours. The verb to like (he likes, they like, it is liked) implies the liking relation.

> Every person likes a colour.

Now every time a person is created, so is a colour which that person will like. If there are two people in the world, the player and Daphne, then we now have five colours: red, green, blue, Daphne's colour and the player's colour. Alternatively, we can assemble the other way around:

> A person likes every colour.

Now we're telling Inform that every time a colour is made, a new person is also made - someone who will like that colour. So this sentence effectively makes three new people, one who likes red, one who likes green, and one who likes blue.

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| Example Being Prepared A kind for jackets, which always includes a container called a pocket. |
RB

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| Example Model Shop An "on/off button" which controls whatever device it is part of. |
RB

Suppose we're particularly mechanically-minded and would like a game in which all of our mechanical devices have buttons to turn them on and off. "Model Shop" An on/off button is a kind of thing. Instead of pushing an on/off button which is part of a switched off device (called the machine): try switching on the machine. Here we are making a rule about how our hypothetical buttons will interact with the machines to which they belong. Instead of pushing... is a rule that pertains to actions, and we will learn more about these in the chapter on actions. "...which is part of a switched off device" provides a specific circumstance - this is only to apply to buttons that are stuck to a machines that can be turned on or off. "(called the machine)" tells Inform that if it finds such a device, it should thereafter refer to it as "the machine." (The called syntax is explained further in the chapter on Change.) A set of three more rules will complete our instructions about using buttons to control devices: Instead of pushing an on/off button which is part of a switched on device (called the machine): try switching off the machine. Instead of switching on an on/off button which is part of a device (called the machine): try switching on the machine. Instead of switching off an on/off button which is part of a device (called the machine): try switching off the machine. Then we hand out buttons with a free hand: One on/off button is part of every device. The Model Shop is a room. A model train is a fixed in place device in the Model Shop. A toy elephant is a device in the Model Shop. Every turn when the model train is switched on: say "The model train circles your feet, blowing small puffs of steam." Every turn when the toy elephant is switched on: say "The toy elephant waves its trunk at you." Test me with "push model train's button / push elephant's button / g / switch off model train's button". And now the game will have a model train's button and a toy elephant's button. It may be that we want (as an added nuance) to add other names for these items. While we would want an assembly to create objects such as "Lucy's hand" and not "Lucy hand", it is entirely reasonable to want to talk about the model train button or the elephant button. We could define these additional names like so: Understand "elephant button" or "button on elephant" as the elephant's button. Understand "model train" or "model" or "train" as "[train]". Understand "[train] button" or "button on [train]" as the model train's button. In the second case, we are defining [train] to mean any of the three phrases "train", "model", and "model train"; so "[train] button" will match "model train button" or "train button" or "model button" equally well. See the chapter on Understanding for more on how to create alternative phrasings for the player to use.

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| Example The Night Before Instructing Inform to prefer different interpretations of EXAMINE NOSE, depending on whether the player is alone, in company, or with Rudolph the Red-nosed Reindeer. |
RB

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| Example U-Stor-It A "chest" kind which consists of a container which has a lid as a supporter. |
RB

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