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§7.4. Barter and Exchange
By default, Inform characters are a bit grudging about giving and sharing objects: they react with disinterest when they're shown things and refuse everything they're offered.
If we'd like to change this, we can simply remove the default "block giving" rule, as in
The block giving rule is not listed in the check giving it to rules.
If we do this, giving items to characters will have the result of moving our possessions to the other person's inventory. Of course, without more customization, the player may not ever be able to persuade the other character to return his possessions. Bribery demonstrates a scenario in which a character will accept gifts if they are interesting to him, and respond with a changed attitude to the player.
Barter Barter expands further on this by allowing other characters to trade things with one another.
See Modifying Existing Commands for ways to allow the player to give or show things that he isn't currently holding
See Actions on Multiple Objects for an implementation of giving that allows the player to offer multiple objects at once, where their combined value determines whether they are accepted
See Money for ways to keep track of cash flow, physical money objects, and price negotiations
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If we want to rewrite the functionality of a command that usually ends with a "block..." rule, we will have to begin by turning the blocking off.
As it happens, correct behavior is built into the GIVE command once "block giving" is turned off, so we do not have to write a replacement report or carry-out rule; the object will be transferred to the possession of the caterpillar. But we do want to adjust the action just a little so that our gift cheers up the recipient:
Now whenever we give something to an animal, the animal will be pleased about the present. Of course, we might also want to add a check rule to giving, to see whether the offering is something the recipient really wants:
There is already a perfectly workable report rule that will describe what happens when we give something to someone, but let's say we want to report on the recipient's changed mood, too:
And the rest is all scenario:
The Leaf Face is above the branch. "The smooth and shiny surface of the leaf extends forward from here, but you have lost the scent-trail. This is not the way home." The pear fragment is an edible thing in Leaf Face. The dead aphid is a thing in Leaf Face.
By default, if we make no modifications, telling one player to give something to another will fail, even if persuasion succeeds. This is because the default behavior of the GIVE command is interrupted by the "block giving rule" -- since in many cases we do not want people to exchange objects freely.
However, suppose that we do want characters to be able to exchange articles freely: we allow persuasion to succeed and turn off the "block giving rule".
And now we might want to implement a way to keep track of whether the recipient character wants what's being offered:
Unsuccessful attempt by someone trying doing something:
if the reason the action failed is the sneering refusal rule, say "'Would you care for [the noun]?' [the person asked] asks solicitously of [the second noun].
Since we've defined this as a relation, we could change what the characters like and dislike during the course of the game, freely; for instance, characters might grow hungry and suddenly like all the edible articles.