| 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 then 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 then change the lantern to switched off;
> if the lantern was switched off then change the lantern to 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.

119
| Example Tense Boxing An overview of all the variations of past and present tenses, and how they might be used.

120
| Example Bruneseau's Journey A candle which reacts to lighting and blowing actions differently depending on whether it has already been lit once.

"Sire," said the Minister of the Interior to Napoleon, "yesterday I saw the most intrepid man in your Empire." - "What man is that?" said the Emperor brusquely, "and what has he done?" - "He wants to do something, Sire." - "What is it?" - "To visit the sewers of Paris." This man existed and his name was Bruneseau. - Victor Hugo, Les Miserables Let's say that our intrepid explorer has a candle that can be lit and blown out again, and should accordingly appear unlit, burning, or partly burnt: "Bruneseau's Journey" The Sewer Beneath St Denis is a room. "A narrow, stone-lined passageway, with only a little ledge to walk above the level of the refuse that flows down towards the Seine." The candle is carried by the player. The description of the candle is "A candle, [if the candle has been lit]partially burnt[otherwise]still in pristine condition with untouched wick[end if]." Instead of examining the lit candle, say "It burns with a pure heart." The block burning rule is not listed in the check burning rules. Instead of burning the lit candle: say "The candle is already lit." Check burning: if the noun is not the candle, say "[The noun] cannot profitably be set on fire." Carry out burning the candle: now the candle is lit. Report burning: if the candle had been lit, say "You relight the candle."; otherwise say "You light the candle for the first time.". Understand "blow out [something]" as blowing out. Understand "blow [something] out" as blowing out. Blowing out is an action applying to one thing. Carry out blowing out the candle: now the candle is unlit. Report blowing out: if the noun is the candle and the candle was lit, say "You blow out [the noun]."; otherwise say "You blow on [the noun], to little effect." Test me with "x candle / light candle / x candle / blow out candle / x candle". We must be careful: "if the noun was lit" would throw errors because past-tense rules can only be applied to specific items, not to variables that could be anything.

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