11.11. Repeat running through

Inform is not used very much for numerical work, so the kind of repeat loop described in the previous section is not much used. Inform's natural domain is really the world of things and rooms, so the following kind of repeat is much more useful.

repeat with (a name not so far used) running through (description of values):

This phrase causes the block of phrases following it to be repeated once for each value matching the description, storing that value in the named variable. (The variable exists only temporarily, within the repetition.) Example:

repeat with item running through open containers:
...

If there are no containers, or they are all closed, the phrases will not be followed at all. Inform will issue a Problem message if the range of the loop may be infinite: for example, it won't allow:

repeat with X running through odd numbers:
...

On the other hand it will allow:

repeat with T running through times:
...

which repeats 1440 times, starting with T at midnight and finishing at 11:59 PM. See the Kinds index for which kinds of value can be repeated through.

As with counting the "number of ..." objects satisfying some property, we can run through a wide variety of possibilities - any description whose range is possible for Inform to search. For example:

One small note of caution: if what the "repeat" loop does is to change the things being repeated through, changing in particular whether items not yet reached will qualify to be repeated through, the results can be unexpected. Rather than writing "repeat with X running through D", it may be safer to try "while there is D (called X)", though note that this will only finish if X is always changed so that it no longer qualifies.

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ExampleStrictly Ballroom
People who select partners for dance lessons each turn.

Many simple repetitions can effectively be done with a "now..." instruction: it is quicker to say

now every person is angry

than

repeat with offended party running through people:
now the offended party is angry.

Repeat comes in handy when we have something a bit more complicated to do with each item:

"Strictly Ballroom"

A person can be alert or occupied. A person is usually alert.

When play begins:
now the player is occupied.

Dance is a kind of value. The dances are waltzes, polkas, cha-chas, charlestons, fox-trots, tangos, lambadas, and two-steps.

The current round is a dance that varies.

Manner is a kind of value. The manners are swiftly, primly, energetically, suavely, seductively, elegantly, and badly.

Every turn: now the current round is a random dance.

Every turn:
    repeat with dancer running through people who are not the player:
        if dancer is alert:
            now dancer is occupied;
            let partner be a random alert person who is not the dancer;
            if partner is a person:
                now partner is occupied;
                say "[The dancer] [the current round][if a random chance of 1 in 5 succeeds] [a random manner][end if] with [partner]. ";
            otherwise:
                say "[paragraph break][The dancer] is forced to be a wallflower. Poor [dancer]. ";
    say paragraph break.

Notice we did not say "repeat with dancer running through alert people who are not the player...". This is because Inform would draw up a list of alert people at the beginning of the repeat, and not take into account which people became occupied partway through the repetition. If we want to make sure that each person dances only with one other person, we have to continue checking alertness each time we run through the repetition.

After all the partners are assigned, we can set up for the next turn by making everyone alert again, and for this we do not need "repeat":

Every turn: now every person is alert; now the player is occupied.

Before doing something to someone: now the noun is occupied.

Before doing something when the second noun is a person: now the second noun is occupied.

Instead of doing something to someone: say "You successfully distract [the noun]."

The Pacific Ballroom is a room. "A rather utilitarian space at the moment, since this is a class and not a party." Timmy, Tommy, Joey, George, Mary, Martha, Yvette, McQueen, Linus, and Patricia are people in the Pacific Ballroom.

Test me with "z / ask linus about blanket / z / z".

	Start of Chapter 11: Phrases
	Back to §11.10. Repeat
	Onward to §11.12. Next and break