A SNePS Approach to The Wumpus
World Agent
or Cassie Meets the Wumpus
Stuart C. Shapiro & Michael Kandefer
Department of Computer Science and Engineering,
and Center for Cognitive Science
University at Buffalo, The State University of New York
201 Bell Hall, Buffalo, NY 14260-2000
{shapiro|mkw3}@cse.buffalo.edu
http://www.cse.buffalo.edu/~{shapiro|mkw3}/
: perform get(gold)
No breeze here.
No stench here.
Exploring the cave...
Found a safe room...
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I am in room (1, 0), facing east
No breeze here.
No stench here.
Exploring the cave...
Found a safe room...
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I am in room (1, 1), facing south
I feel a breeze.
No stench here.
Exploring the cave...
Found a safe room...
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I am in room (0, 1), facing west
No breeze here.
No stench here.
Exploring the cave...
Found a safe room...
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I am in room (0, 2), facing south
I feel a breeze.
No stench here.
Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Found a safe room...
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I am in room (2, 0), facing east
I feel a breeze.
No stench here.
Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
Visiting an old room...
This is boring.
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Exploring the cave...
I'll chance a move...
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I am in room (1, 2), facing south
No breeze here.
I'm grabbing for the gold.
No stench here.
I'm going home!
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Score = 966.
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Formalism Used
• SNePS KRR system
• SNeRE acting subsystem
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Strategy
• Wander semi-randomly until find gold
– Opportunistically shoot the wumpus
• Grab the gold
• Go home
• Stop
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Semi-Random Exploration
• If have an adjacent safe new room, go there
• Else if totally bored,
– Risk going to any adjacent new room
• Might die!
– If none move randomly (boring)
• Else go to an old room (boring)
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Finding Home
• Lay down VisitedFrom(r2, r1) “arrows”
while exploring.
• No two with same r2 to cut loops.
• Follow backwards to find home.
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Finding Walls
• Two walls adjacent to home room known
• When bump, believe wall location
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Important SNePS Features 1
• First-person beliefs
– Not third-person “truth” about agent or world
• Beliefs are current beliefs
– Even if about the past
• On-line acting
• Reified propositions as well as acts & …
• Neither states nor times are privileged
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Important SNePS Features 2
• SNeRE acts with operational semantics
– External acts:
• go(right)
• do(grab)
• senseFor(breeze)
– Control acts:
• snsequence(go(right), go(right))
– Mental acts:
• believe(p)
• disbelieve(p)
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Important SNePS Features 3
• SNeRE policies integrate reasoning & acting
– whendo(See(glitter), do(grab))
– ActPlan(find(home),
snif({if(In(cell(0,0)), do(stop)),
else(…)}))
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Important SNePS Features 4
Use of SNePS andor connective
and belief revision
for state constraints:
andor(1,1){Facing(north), Facing(south),
Facing(east), Facing(west)}
Facing(east)
=> ~Facing(north), ~Facing(south), ~Facing(west)
believe(Facing(south))
Facing(south), ~Facing(north),
~Facing(east), ~Facing(west)
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Important SNePS Features 5
Nondeterministic Choice
~Have(gold)
=>(all(r1)(In(r1)
=> ActPlan(explore(cave),
withsome({?r2, ?d1},
SafeNewRoom(r1, ?r2, ?d1),
snsequence3(turn(?d1),
move(forward),
believe(Bored(0))),
<else clause>))))
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Important SNePS Features 6
Numerical Quantifier
wheneverdo(Feel(breeze),
withsome/3(?r, In(?r),
believe(nexists(1,4,4)(c)({Adjacent(?r,c)}:
{Contains(c,pit)}))))
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Problems
• The SNePS control structure
–
–
–
–
–
Asynchronous
Multiprocessing
Producer/consumer
Message passing
Focused bidirectional inference
• Made designing the agent,
viewed as a programming task,
somewhat difficult.
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