9.13. The past and perfect tenses

| Chapter 9: Time |

| 9.13. The past and perfect tenses

The remaining sections of this chapter go into more technical ways to think about the progress of the game through time, and can be skipped at a first reading.

Conditions are clauses which require Inform to make a decision: is such-and-such true, or not true? We have already seen conditions attached to rules using "when":

> Instead of waiting when the Sorting Hat is in the Hall: ...

and, as we shall later see, we will often want to write instructions like:

> if the Sorting Hat is in the Hall, say "Hermione blinks apprehensively."

The condition is "the Sorting Hat is in the Hall", and during play this will sometimes be true and sometimes false.

A condition in the form "X is Y" is of course written the present tense, and refers to the current state of affairs. Three other tenses are allowed. First, the present perfect:

> if X has been Y ...

is true if it has ever been the case that "X is Y" at the start of any turn (or any action). So, for instance,

> if the gate has been open ...

will be valid if and only if the gate has ever been made open by any action (even if it is closed now), or if it started out by being open when play began.

Next is the past tense:

> if X was Y ...

holds if and only if "X is Y" was true at the start of the most recent action. This is convenient when trying to describe what has changed in the course of the action, but sometimes also when making the action itself happen. For instance:

> if the lantern was switched on, now the lantern is switched off;
> if the lantern was switched off, now the lantern is switched on;

Completing the set is the past perfect:

> if X had been Y ...

which records whether "X has been Y" was true at the start of the most recent action. All these verbs can of course be negated (though "wasn't" and "hadn't" are disallowed as poor style: we use "was not" and "had not" instead). So for example,

> if the player had not been in the Ballroom ...

is true if the player hadn't visited the Ballroom at the start of the most recent action.

Something we must watch out for is that variables might not have the same values in the past that they have now. As a result, writing conditions such as "if the noun has been open" is a bad idea, because in the past "the noun" very likely referred to something different. It is really only safe to talk in the past tense about definite, fixed things: "if the Great Gates of Kiev have been open" would be fine.

149
| Example Tense Boxing An overview of all the variations of past and present tenses, and how they might be used. |
RB

150
| Example Elsie A door that closes automatically one turn after the player opens it. |
RB

Suppose we want to create an automated door of the sort that closes when it isn't in use. A convenient way is to write a rule that fires "every turn when the sliding door was open". This will be true only if the door was open at the beginning of the turn: if the player just opened it this turn, it stays open, and if it was already closed, it stays closed. Thus: "Elsie" The axis-ward is a direction. The opposite of axis-ward is hub-ward. Understand "aw" or "axisward" as axis-ward. The hub-ward is a direction. The opposite of hub-ward is axis-ward. Understand "hw" or "hubward" as hub-ward. The Ship's Bridge is a room. The sliding door is a door. It is axis-ward from Bridge and hub-ward from C Deck. The initial appearance is "There is a door in this wall[if closed] -- or at least, the potential for a door, since currently it is sealed, distinguishable from the rest of the wall only by the warning stripes on its surface[end if]." Every turn when the sliding door was open: now the sliding door is closed; if the player can see the sliding door: say "The sliding door slips back into place, sealing the wall as though there had never been a breach." After opening the sliding door: say "You press the appropriate buttons, and a section of wall slides away." Test me with "open door / look / enter door / z".

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| Example Bruneseau's Journey A candle which reacts to lighting and blowing actions differently depending on whether it has already been lit once. |
RB

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