# TIAAction

## Overview

The purpose of the tiaaction.t extension is to allow game authors to define actions involving three objects, such as PUT COIN IN SLOT WITH TWEEZERS. Note that you only need this extension if you want to define an action involving three physical objects. Actions involving two objects and a literal or topic, say, can be defined using other techniques.

## New Classes, Objects and Properties

In addition to a number of properties intended purely for internal use, this extension defines the following new classes, objects and properties:

- Classes: TIAAction.

## Usage

Include the tiaaction.t file after the library files but before your game source files. This will allow you to define actions involving three objects. The macros needed to support this are already defined in advLite.htm for your convenience.

The third object involved in a three-object command is the Accessory Object, normally abbreviated to aobj (although in many contexts the abbreviation acc may also be used, since this is what is used by the Mercury parser on which adv3Lite is based). Thus, for example, do refer to the accessory object of the current command you'd use gAobj. To define action handling on an object in its role as accessory object you'd use aobjFor(WhateverAction). In a message parameter substitution you'd use aobj to refer to the accessory object (e.g. {the aobj} or {the subj aobj}). In a VerbRule you'd use singleAobj or multiAobj (in practice nearly always the former) as the marker for the accessory object in the player's command, and when defining a TIAAction you'd use the DefineTIAAction() macro. You use all these in much the same way as you'd use the dobj and iobj equivalents when defining a new TIAction.

This is best explained by means of an example. Suppose we wanted to implement an action that could handle commands of the form PUT COIN IN SLOT WITH TWEEZERS. First we'd define the action and its associated VerbRule:

    DefineTIAAction(PutInWith)
    ;

    VerbRule(PutInWith)
        'put' multiDobj 'in' singleIobj 'with' singleAobj
        : VerbProduction
        action = PutInWith
        verbPhrase = 'put/putting (what) (in what) (with what)'
        missingQ = 'what do want to put; what do you want to put it in;
            what do you want to put it in with'
    ;

Next, we'd define the default handling for this new action on the Thing class, as normal. In this simple example we'll assume that PutInWith acts much like PutIn, except that by default we can't use a Thing to put other things in with:

     modify Thing
        dobjFor(PutInWith) asDobjFor(PutIn)
        iobjFor(PutInWith) asIobjFor(PutIn)
        aobjFor(PutInWith)
        {
            preCond = [objHeld]

            verify()
            {
                illogical('{I} {can\'t} use {the aobj} to put anything anywhere. ');
            }
        }
    ;

Finally, we'd probably go on to define the slot, the coin and tweezers in such a way that the player has to use the tweezers to put the coin in the slot:

    + coinSlot: Container, Fixture 'coin slot'
        bulkCapacity = 1

        notifyInsert(obj)
        {
            if(obj != coin)
            {
                "Only a coin will fit in that slot. ";
                exit;
            }
            if(gAobj == nil)
            {
                "It's too fiddly to put the coin in the slot with your fingers. ";
                exit;
            }

            inherited(obj);
        }
    ;

    + coin: Thing 'coin; worn'
        "It's very worn. "
        initSpecialDesc = "A coin lies on the ground. "
    ;

    + tweezers: Thing 'tweezers;;;them'
        aobjFor(PutInWith)
        {
            verify()
            {
                if(gDobj == self)
                    illogicalSelf('{The subj dobj} {can\'t} be used to manipulate
                        themselves. ');
            }

            check()
            {
                if(gDobj.bulk > 1)
                    "{The subj dobj} {is} too large to be manipulated with {the
                    aobj}. ";
            }
        }
    ;

This covers most of what you need to know to use this extension. For additional information see the source code and comments in the tiaaction.t file.

Adv3Lite Manual
Table of Contents | Extensions > TIAAction
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