The TADS Alternate Library
Version 2.0

List Grouping

Copyright 2000 by Kevin Forchione.
This is part of the TADS Alternate Library Authors Manual.

List Grouping[1]

The Alt general listing produced by listContGen() is capable of producing a variety of general listings including the following:

HTML TADS - A multimedia TADS 2.5.2 Interpreter.

Welcome to TADS Alternate Library...

Sample Game

An Interactive Fiction

Release 1 / Serial number 000404

Alt Library Version 1.0.2

Entryway

This large, formal entryway is slightly intimidating: the walls are lined with somber portraits of gray-haired men from decades past; a medieval suit of armor, posed with battle axe at the ready, towers over a single straight-backed wooden chair. The front door leads back outside to the south. A hallway leads north. There is a small sign here.

The glass bottle is open.

There's a beach ball here.

The front door is closed.

You can also see 3 hats (one fez, one Panama, and one sombrero); 9 coins (four silver, two bronze, and three gold); and the letters X, Y, and Z from a Scrabble set here.

The last line of this listing demonstrates Alt List Grouping. This feature allows an author to sublist objects according to abstract groupings such as “hats” or “coins” and to prefix and suffix these sublist with messages and counts. Objects which are listed together are displayed thus anytime they are presented through listContGen(). They are even listed together in for aggregate display purposes:

>take gold and silver coins

5 coins (one gold and four silver): Taken.

The ListGroup Class

To use this special feature you need to create a ListGroup object. Next give your game objects a listTogther attribute that points to this ListGroup object. Finally provide each object with the groupDesc and groupPluralDesc attribute used to describe itself when it appears in a ListGroup sublist.

For example, to produce the list group display for the Scrabble pieces above, we defined the following:

scrabbleTileListGroup: ListGroupMessage

groupPrefix = "the letters "

groupSuffix = "from a Scrabble set"

;

class ScrabbleTile: Item

listTogether = scrabbleTileListGroup

sDesc = "Scrabble letter <<groupDesc>>"

adjective = 'letter'

plural = 'letters'

;

x: ScrabbleTile

location = entryway

groupDesc = "X"

noun = 'x'

;

y: ScrabbleTile

location = entryway

groupDesc = "Y"

noun = 'y'

;

z: ScrabbleTile

location = entryway

groupDesc = "Z"

noun = 'z'

;

Alt provides a general ListGroup class and two more specialised classes: ListGroupMessage and ListGroupParenCount an author can use as superclasses for their ListGroup object.

ListGroupMessage: This class prefixes the sublist with the object’s groupPrefix and suffixes the list with the groupSuffix. Display takes the form groupPrefix <sublist> groupSuffix.

ListGroupParenCount: This class prefixes the sublist with a count of the objects in the sublist, followed by the groupPrefix, followed by a parenthesis, then the sublist, another parenthesis, and finally the groupSuffix. Display takes the form sublistCount groupPrefix ( sublist ) groupSuffix.

An example, using the ListGroupParenCount class:

coinListGroup: ListGroupParenCount

groupPrefix = "coins"

;

class SilverCoin: Item

location = entryway

isEquivalent = true

plural = 'coins'

noun = 'coin'

adjective = 'silver'

sDesc = "silver coin"

pluralDesc = "silver coins"

groupDesc = "silver"

pluralGroupDesc = "silver"

listTogether = coinListGroup

;

coin1: SilverCoin;

coin2: SilverCoin;

coin3: SilverCoin;

coin4: SilverCoin;

class BronzeCoin: Item

location = entryway

isEquivalent = true

plural = 'coins'

noun = 'coin'

adjective = 'bronze'

sDesc = "bronze coin"

pluralDesc = "bronze coins"

groupDesc = "bronze"

pluralGroupDesc = "bronze"

listTogether = coinListGroup

;

coin5: BronzeCoin;

coin6: BronzeCoin;

class GoldCoin: Item

location = entryway

isEquivalent = true

plural = 'coins'

noun = 'coin'

adjective = 'gold'

sDesc = "gold coin"

pluralDesc = "gold coins"

groupDesc = "gold"

pluralGroupDesc = "gold"

listTogether = coinListGroup

;

coin7: GoldCoin;

coin8: GoldCoin;

coin9: GoldCoin;

This produces the display: 9 coins (four silver, two bronze, and three gold).

The groupPrefix and groupSuffix Attributes

The ListGroup object may define a groupPrefix and groupSuffix for the sublist. Both the ListGroupMessage and ListGroupParenCount class do not display the groupPrefix or groupSuffix when the sublist consists of one set of objects, even if that set consists of multiple indistinguishable objects. For example, if we take the gold coins and check our inventory:

>take gold coins

three gold coins: Taken.

You have a rucksack (being worn) and three gold coins.

The gold coins are displayed normally. But if we take the bronze coins and check our inventory:

>take bronze coins

two bronze coins: Taken.

You have a rucksack (being worn) and 5 coins (three gold and two bronze).

The coins are listed together using their ListGroup object definition.

The groupDesc and groupPluralDesc Attributes

Every thing class object inherits groupDesc and groupPluralDesc attributes. The groupDesc attribute default is sdesc, while the groupPluralDesc default is pluraldesc. Use the groupDesc and groupPluralDesc attributes to describe the objects as you wish them to appear in the ListGroup sublist. When objects are not grouped in a ListGroup display or the sublist of the ListGroup consists of only one set of objects then they are displayed using the normal rules for listContGen().

For instance, in our coin example above, if all we are holding are the bronze coins then when we check our inventory we see:

You have two bronze coins.

which is what we would expect, rather than “You have two bronze”. Using groupDesc and groupPluralDesc allows an author to tailor the sublist display flexibly.

[1] We are greatly indebted to Michael J. Roberts for outlining much of the details of the ListGroup class, and for providing sample coding demonstrating how it should work.