2.1.  Objects

     As	in most	Adventure-like	games,	the  most  important
data  type in ADL is the Object.  An object in real life can
be a person, place, or thing.  ADL models the world  in	 the
same   way.    Any  Object  encountered	 by  the  player  is
represented by this  type,  as	are  all  locations  in	 the
scenario.  Indeed, there can be	Objects	associated with	peo-
ple (more on  that  later).   Notice  that  ADL	 treats	 all
Objects	 uniformly and so it is	possible to write a scenario
in which a player picks	up an Object (a	tent, say),  carries
it around, and later enters it.

     All Objects are  represented  by  (unique)	 sixteen-bit
integers.   This  number  is known as the "Object ID" of the
Object.	 Objects are (essentially)  record  structures	with
the following elements:

Location      The Object ID of	the  Object  which  contains
	      this Object.

Contents      The Object ID of the  first  Object  which  is
	      contained	 in this Object, or zero if there is
	      no such Object.

Link	      The Object ID of	the  next  Object  which  is
	      located  in  the	same place as this Object or
	      zero if there is no such Object.

Modifier      The ID of	the modifier of	this Object or	zero
	      if  the  Object has no modifier.	For example,
	      the Object "blue streak" would have a modifier
	      ID  which	 is the	adjective "blue".  Modifiers
	      are explained further in Section 2.9.

Properties    Associated with each Object are 32 properties.
	      While all	of the above elements are maintained
	      directly or indirectly by	the ADL	system,	 the
	      values  and  meanings  of	 properties  are the
	      responsibility of	the programmer.	  The  first
	      16 of these properties may only hold the value
	      0	 or  1	(hence	they  are   usually   called
	      "boolean"	 properties).  Properties 17 through
	      32 may  hold  any	 value	between	 -32768	 and
	      32767.   The  last  three	 of these properties
	      have special meaning to ADL:

	      LDESC  (30)   This is  the  ID  of  a  routine
			    which  prints  a "long" descrip-
			    tion of  the  Object.   Routines
			    are	defined	in Chapter 6.

	      SDESC  (31)   This is  the  ID  of  a  routine
			    which  prints a "short" descrip-
			    tion of the	Object.

	      ACTION (32)   This is  the  ID  of  a  routine
			    which  is  called under the	cir-
			    cumstances detailed	 in  Chapter
			    4.

     All Objects in ADL	are stored in a	tree.  The root	node
of  the	tree is	predeclared and	is named ".ALL".  Its Object
ID is always zero.  All	other Objects are ultimately located
in .ALL.

     Two other predeclared  Objects  exist.   One  is  named
"STRING"  and the other	is named ".ME".	 .ME is	not truly an
Object -- it is	more like a variable  which  represents	 the
current	 Actor	during the execution of	an ADL program (more
on Actors in Section 3.1).  It is illegal to use .ME outside
of  the	context	of a routine.  STRING is the Object which is
seen by	the ADL	program	when the  run-time  sentence  parser
encounters  a  string.	 Note that although STRING is prede-
clared by ADL, the properties of STRING	must be	 defined  by
the  ADL  programmer.  See Chapter 9 for more information on
STRING.