Hatless

Example 126
★★

It's tempting to use "now…" to distribute items randomly at the start of play, but we need to be a little cautious about how we do that.

Suppose we want a game in which each scenario starts with the characters wearing hats – randomly passed out. We might be tempted to write our scenario like this:

"Hatless"
The Costumery is a room. Larry, Curly, and Moe are men in the Costumery. Janine is a woman in the Costumery.
Rule for writing a paragraph about a person (called the target) who wears a hat (called attire):
   say "[The target] is here, looking stylish in [an attire]."
Rule for writing a paragraph about a hatless person (called the target):
   say "[The target] mopes about, hatless."
A hat is a kind of thing. A hat is always wearable. Definition: a person is hatless if he is not the player and he does not wear a hat.
The indigo bowler, the polka-dotted fedora, the pink beret, and the scarlet cloche are hats.
When play begins:
   now every hat is worn by a random hatless person.

And we might hope that this would choose a new hatless person for each hat, but we would be wrong. It will instead choose one hatless person and put all the hats on him – and everyone else has to go bare-headed. That's clearly no good. Let's try again:

"Hatless 2"
The Costumery is a room. Larry, Curly, and Moe are men in the Costumery. Janine is a woman in the Costumery.
Rule for writing a paragraph about a person (called the target) who wears a hat (called attire):
   say "[The target] is here, looking stylish in [an attire]."
Rule for writing a paragraph about a hatless person (called the target):
   say "[The target] mopes about, hatless."
A hat is a kind of thing. A hat is always wearable. Definition: a person is hatless if he is not the player and he does not wear a hat.
The indigo bowler, the polka-dotted fedora, the pink beret, and the scarlet cloche are hats.
When play begins:
   now every hatless person wears a random hat.

But this selects one random hat and assigns it to each hatless person in turn – so it will only wind up being worn by the last of them (since Inform knows that only one person can wear a hat at a time).

In this case, we do have to expand out our loop so that the game makes an explicit distribution:

"Hatless 3"
The Costumery is a room. Larry, Curly, and Moe are men in the Costumery. Janine is a woman in the Costumery.
Rule for writing a paragraph about a person (called the target) who wears a hat (called attire):
   say "[The target] is here, looking stylish in [an attire]."
Rule for writing a paragraph about a hatless person (called the target):
   say "[The target] mopes about, hatless."
A hat is a kind of thing. A hat is always wearable. Definition: a person is hatless if he is not the player and he does not wear a hat.
The indigo bowler, the polka-dotted fedora, the pink beret, and the scarlet cloche are hats.
When play begins:
   repeat with item running through hats:
      now the item is worn by a random hatless person.

Each time Inform considers the instruction "now the item is worn by a random hatless person", there is one fewer such person to choose from – so we can guarantee that the hats are distributed one per customer and that all hats are distributed.

Hatless 3 is only guaranteed to work because the number of hats is less than or equal to the number of people; otherwise the final use of random will return "nothing" and then a problem message will appear during play.