3.1.  Actors

     In	a typical adventure game it seems as if	 the  player
is  moving  around the dungeon taking things, smelling them,
breaking them, and so on.  A better model would	be that	 the
player	is  giving  commands  to  an actor.  It	is the actor
which actually moves around, collects items,  and  otherwise
acts.  It is this model	which ADL follows.

     An	Actor is essentially an	"animate" object which	acts
upon  commands given to	it.  Notice that there is nothing in
this model which prevents more than one	Actor  from  running
around	a  scenario.  In fact, in ADL there may	be up to ten
Actors which are active	at any one time.

     There are two kinds of Actors:   interactive  and	non-
interactive.   The  player  is	an example of an interactive
Actor.	Commands are read directly  from  the  keyboard	 and
placed	in  a line buffer which	is then	passed to the parser
and interpreter.  When the line	buffer is empty	a new one is
read  from  the	 keyboard.   Any  number  of  Actors  may be
interactive, making multiple player games a possibility.

     The robot in the introductory script is an	example	of a
non-interactive	 Actor (see Appendix 2 for the source to the
scenario which produced	that script).  The line	 buffer	 for
the  robot  was	 initialized after the player typed the	sen-
tence starting with "Tell the robot ...".   The	 robot	then
acted on this command by performing the	requested actions in
parallel with the actions of the player.   This	 means	that
each  Actor  gets  one	turn  for  each	turn that the player
experiences.  A	non-interactive	Actor is  deleted  from	 the
list of	active Actors when its line buffer is emptied.

     There is a	special	object-like item named ".ME" used to
implement  this	 sort  of "multiprocessing".  .ME represents
the Object ID of the current Actor for the purposes of	mov-
ing  around,  taking  things, etc.  Anything that the player
can do can be done just	as well	by another Actor.   This  is
probably  the  most  powerful  (and most obscure) feature of
ADL.

     Actors may	be activated using the $actor built-in	rou-
tine and deleted at any	time by	using the $delact routine.