Page 149 - Concise Encyclopedia of Robotics

“HACKER” PROGRAM H
One of the earliest experiments with artificial intelligence (AI) was done
with an imaginary robot, entirely contained within the “mind” of a
computer. A student named Gerry Sussman wrote a program called
“Hacker,” in a computer language known as LISP. The result was a little
universe in which a robot could stack blocks on each other.
Sussman created laws of physics in the imaginary universe. Among
them were things such as
• Blocks X, Y, and Z each weigh 5 lb.
• Blocks V and W each weigh 50 lb.
• The robot can lift no more than 10 lb.
• Only one object can occupy a given space at a given time.
• The robot knows how many blocks there are.
• The robot can find blocks if they are not in direct sight.
Illustration 1 shows the five blocks lying around, as they might appear on
the computer monitor, along with the robot.
Sussman gave commands to the robot, such as, “Stack the blocks all
up,one on top of the other.”As stated,this command is impossible,because
it requires the robot to lift a block weighing 50 lb (either V or W), and the
robot is capable of lifting only 10 lb (see illustration 2). What would
happen? Would the robot try forever to lift a block beyond its limit of
strength? Or would it tell Sussman something like, “Unable to do this”?
Would it go after either block V or W first, trying to get it on top of one
of the lighter blocks, or on top of the other heavy block? Would it pick up
all the lighter blocks X,Y,and Z in some sequence,stacking them vertically
on top of V or W? Would it put two light blocks on V, and the remaining
light block on W, and then give up? Eventually, the robot would run into
the impossibility of the command. But how long would it try, and what
would it try, before quitting?


Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.