-- -*- Mode: Sather;  -*-
-- File: creature.sa
-- Author: Chu-Cheow Lim (clim@ICSI.Berkeley.EDU)
-- Copyright (C) International Computer Science Institute, 1993
--
-- COPYRIGHT NOTICE: This code is provided "AS IS" WITHOUT ANY WARRANTY
-- and is subject to the terms of the SATHER LIBRARY GENERAL PUBLIC
-- LICENSE contained in the file: "sather/doc/license.txt" of the Sather
-- distribution. The license is also available from ICSI, 1947 Center
-- St., Suite 600, Berkeley CA 94704, USA.
--*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--* FUNCTION:
--*
--* CLASSES:
--* 
--* REQUIRED FILES:
--*
--* RELATED FILES:
--*
--* HISTORY:
--* Last edited: Jun  1 16:17 1993 (clim)
--* Created: Fri May 21 12:08:08 1993 (clim)
--*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class ABSTRACT_CREATURE is
   -- Abstract ancestor class of "SHARK" and "FISH".

   shared breed_age:INT := 10;
   -- Breeding age to be re-determined by each descendent.

   age:INT;			-- Age.
   pos_x,pos_y:INT;		-- Position.
   -- Instead of using COMPLEX, we could use integers for the creature position
   -- when the grid is discretized.
   -- Eg of extensibility:
   --  * Suppose the position is continuous instead of discrete, then only
   --    the definitions in "ABSTRACT_CREATURE" need be changed.
   
   create(x,y:INT):SELF_TYPE is
      -- Allocate a creature at (x,y) position.
      res := new;
      res.pos_x := x;
      res.pos_y := y;
   end; -- create

   init(x,y:INT) is
      -- Initialize creature's attribute ((x,y) position in this case).
      update_pos(x,y);
   end; -- init

   update_pos(x,y:INT) is
      pos_x := x;
      pos_y := y;
   end; -- update_pos

end; -- class ABSTRACT_CREATURE

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class ABSTRACT_PREDATOR is
   ABSTRACT_CREATURE;
   shared starve_time:INT := 1;
   -- Length of time that a predator can go on without eating.

   starve_age:INT;
   -- Predators have an additional attribute that indicates how long one has been
   -- starving.
end; -- class ABSTRACT_PREDATOR

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class ABSTRACT_PREY is
   ABSTRACT_CREATURE;
end; -- class ABSTRACT_PREY

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class SHARK is
   ABSTRACT_PREDATOR;

   shared breed_age:INT := 10;
   shared starve_time:INT := 1;
   -- Length of time that a shark can go on without eating.
   
   create(x,y:INT):SELF_TYPE is
      -- Allocate a shark at (x,y) position.
      res := new;
      res.init(x,y);
   end; -- create

end; -- class SHARK

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

class FISH is
   ABSTRACT_PREY;
   shared breed_age:INT := 1;

   create(x,y:INT):SELF_TYPE is
      -- Allocate a fish at (x,y) position.
      res := new;
      res.init(x,y);
   end; -- create

end; -- class FISH

--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~