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Inform 7 Home Page / Documentation
§6.12. A word about nothing
Like "in", "nothing" has two slightly different meanings, though here there's much less potential for confusion.
Meaning 1. "Nothing" as "no thing". This is the meaning in sentences like:
And similar for conditions like "if the box contains nothing". It's a word which describes the absence of things: it says that, though there might have been many possible items here, it turned out that there were none.
Meaning 2. "Nothing" as a value. This is much less commonly seen, but sometimes Inform stores a value such as a property (or a variable) which always has to be an object. In some circumstances, "nothing" is then a special value meaning that this is not set at present. For instance,
Definition: a container is impossible if its matching key is nothing.
The "matching key" property of a container is always an object, but is allowed to be "nothing" when there isn't a matching key anywhere. (If such a container is locked, nobody will ever be able to unlock it.)
How Inform decides. So which meaning does Inform use, and when? The answer is that it depends on the relationship being talked about. When this is "is", values are being compared and we are using meaning 2. But when it is any other relationship, like "is in" - which talks about containment - then we are using meaning 1.