(IE-0033) Kit-set properties

• Proposal: IE-0033
• Discussion PR link: #33
• Authors: Graham Nelson
• Status: Accepted
• Related proposals: IE-0025
• Implementation: Implemented but unreleased

Summary

Extends the Neptune mini-language to allow kits to assign properties to kinds of object which are invisible from source text, and can thus be used as part of the private low-level implementation for features.

Motivation

Inform already has a way to force all instances of a given kind of object to have certain property values, in a sneak-under-the-radar way, but it is a clumsy feature and one which currently works so crudely that it can only work if stories are compiled via Inform 6, not via C. This is to write, say:

Include (-
	has enterable supporter,
	with max_capacity 10,
-) when defining a rideable animal.

This works very simplistically: when Inform code-generates an Inform 6 class definition for the kind in question, it simply transcribes this text verbatim. If Inform is trying to code-generate a C structure representing the kind, the user is out of luck. In any case, this crude syntax is not really consistent with other uses of Include (- ... -), and the whole point is to express something which is invisible from the point of view of source text: so why is it being done in source text?

The following small feature is intended to replace the Include ... when defining... syntax. Because it is only available from Neptune files, it means that only kits can perform this dubious magic trick, though of course directory-format extensions can now include kits. If this seems a little restrictive, that's intentional, really: it's a feature which should only be used by kits anyway.

Components affected

• No change to the natural-language syntax.
• Minor change to inbuild.
• Minor changes to inform7.
• No change to inter.
• No change to the Inter specification.
• No changes to runtime kits.
• No changes to the Standard Rules and Basic Inform.
• No change to documentation.
• No change to the GUI apps.

Impact on existing projects

None, though on subsequent releases of Inform the Include ... when defining... syntax will be withdrawn, so that extension authors are advised to use the new functionality instead.

Details

The above example use of Include ... when defining... can now be replicated with the following stanza from a Neptune file:

properties of rideable animal {
	attribute: enterable
	attribute: supporter
	property: max_capacity = 10
}

The stanza properties of K { ... } must give the name for K, which must be a valid kind of object (though it can be one with no instances), and can give the name either in the singular or the plural. Inside this stanza, only the following are allowed:

	attribute: ATTRIBUTENAME
	attribute: ~ATTRIBUTENAME
	property: PROPERTYNAME
	property: PROPERTYNAME = NUMBER

The syntax ~ATTRIBUTENAME means the attribute is set to false, not true; this is traditional Inform 6 notation. The short form property: PROPERTYNAME sets the property value to 0.