Run-Time Problem (P31) when running custom listing of only one item in container

Authoring Inform 7
#1

I have a system wherein items are purchased from a special type of container called a stock, which lists its contents in a custom-defined way. Here’s how it works:

"test" by Theo Court

Part 1 - Price

Price is a kind of value. $9999.99 specifies a price. 
A thing has a price. The price of a thing is usually $0.00.
The player carries a coin purse. The coin purse contains money. The price of the money is $10000.00.

Instead of buying something:
	decrease the price of the money by the price of the noun;
	say "You part ways with [the price of the noun], leaving you with [the price of the money] and [the noun].";
	now the price of the noun is $0.00;
	now the player is carrying the noun.

Part 2 - Stocks

A stock is a kind of container.

Instead of examining a stock:
	say "[description of the noun] [line break][line break]";
	if the noun contains more than one thing:
		say "[The noun] contains the following items for sale:";
		repeat with content running through things in the noun:
			say "[line break]- [a content], for [price of content]";
		say "[line break]";
	otherwise if one thing is in the noun:
		say "[The noun] contains [a second noun], for [price of the second noun].";
	otherwise if the noun does not contain anything:
		say "[The noun] is empty."
		
After printing the name of a stock:
	omit contents in listing.
		

Part 3 - The Actual Example

The Garden is a room.
The chest is a stock in the Garden with the description "An unusually sticky chest." 
Some things in the chest are defined by the Table of Dubious Items.

Table of Dubious Items
thing					price
a bottle of vodka		$4.20
a cucumber				$0.69
a length of rope		$6.66
a magic wand			$12.34	


Test me with "x chest/buy vodka/x chest/buy cucumber/x chest/buy rope/x chest/buy wand/x chest"

When I run this example, everything works perfectly… until I x chest after running buy rope (i.e: when there’s exactly one item in the chest.) Buying the wand still works, and then I can examine the chest once again without issue, seeing that it is empty.

Why does this happen?

#2

The second noun is only defined if the action requires it. The examining action has only a noun (the thing examined); it does not have a second noun. Thus, the second noun is set to nothing (a special object), which lacks a price.

You probably want something like:

otherwise if exactly one thing is in the noun:
	let last item be a random thing in the noun;
	say "[The noun] contains [a last item], for [price of the last item].";

which seems to work OK for your test commands.

See WWI 7.10 The noun and the second noun and some background at WWI 12.20 Stored actions. (And also WWI 6.16 Counting while comparing for the keyword “exactly”.)

1 Like
#3

This works perfectly. Thanks!