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01/09/98 LISP Agent Continued

01/09/98 LISP Agent Continued. Administrative PS0 out, PS1 assigned next Monday Last time agent design and demo the top-level agent loop LISP concepts Symbols, including T and NIL Conditionals, including IF and WHEN Lexical variables, including LET and LET*

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01/09/98 LISP Agent Continued

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  1. 01/09/98 LISP Agent Continued • Administrative • PS0 out, PS1 assigned next Monday • Last time • agent design and demo • the top-level agent loop • LISP concepts • Symbols, including T and NIL • Conditionals, including IF and WHEN • Lexical variables, including LET and LET* • Side-effecting and “pure” functions • This time • high-level architecture: percepts, behaviors, macros • code for percepts and behaviors

  2. Matching Agent Behaviors Macro-actions Percepts Truckworld Architecture Overview Behavior selection and execution Macro expansion Action execution Sensing Primitive actions and sensing

  3. Perception • A percept is a record of everything the agent knows about the world at the present time • obviously depends both on the world and on the agent’s sensing capabilities • Truckworld: agent can perceive certain features of • the objects at its current location • the objects it is holding and in its cargo bays • its internal status (fuel, heading, speed, status) • Truckworld sensors return raw sensing reports which must be coalesced into one percept

  4. A Truckworld Sensing Report (SENSOR TRUCK-SENSOR ( ((POSITION 0) (KIND ROADSIGN) (DIRECTION E) ...) ((POSITION 2) (KIND GARBAGE) (VALUE 10)) ((POSITION 3) (KIND GLASS) (COLOR GREEN)) ((POSITION 4) (KIND FUEL-DRUM-DISPENSER)) ((POSITION 5) (KIND ATM)) ((POSITION 6) (KIND GARBAGE-CAN)) ((POSITION 7) (KIND GLASS-RECYCLER)) ((POSITION 8) (KIND FUEL-DRUM-CONSUMER)) ((POSITION 9) (KIND TRUCK) (TRUCK-ID TRUCK-5))) an object an attribute and value a sensor report

  5. Sensor Reports to Percepts • A percept is a collection of sensor reports from • the truck sensor • the two cargo bays • the fuel tank all packaged into one data structure • Support routines we need for percepts • create one from a set of sensor reports • find a fuel-drum-consumer outside • find an empty space in BAY-1 • return the current fuel level

  6. The Percept Data Structure (defstruct percept location-contents bay-1-contents bay-2-contents fuel-level) (defun find-objects (percept kinds location) (case location ((:OUTSIDE) (find-objects-at kinds (percept-location-contents percept))) ((BAY-1) (find-objects-at kinds (percept-bay-1-contents percept))) ((BAY-2) (find-objects-at kinds (percept-bay-2-contents percept))) (OTHERWISE (error "Don't understand location ~a" location))))

  7. Processing Percepts (cont.) (defun find-objects-at (kinds percept-list) (mapcar 'object-position (remove-if-not #'(lambda (object) (member (object-kind object) kinds)) percept-list))) ’(glass garbage) ’((POSITION 0) (KIND ROADSIGN) (DIRECTION E)) ((POSITION 2) (KIND GARBAGE) (VALUE 10)) ((POSITION 3) (KIND GLASS) (COLOR GREEN)) ((POSITION 4) (KIND FUEL-DRUM-DISPENSER)) ((POSITION 5) (KIND ATM)) ((POSITION 6) (KIND GARBAGE-CAN)) ((POSITION 7) (KIND GLASS-RECYCLER)) ((POSITION 8) (KIND FUEL-DRUM-CONSUMER)) ((POSITION 9) (KIND TRUCK) (TRUCK-ID TRUCK-5))))

  8. Definition of object-kind

  9. Summary of percept • A single data structure that captures all sense data • Supports operations like • find me all objects with this kind at this location • find me an empty position at this location • tell me what the fuel level is • Will be created by the sense behavior • Will be examined • in deciding what behavior to do next • in deciding what a chosen behavior should do

  10. Behaviors • A behavior is a mapping from a percept to a (macro)action. • a macro-action is a fixed sequence of Truckworld primitives, like • pick up the object at position 3 outside using ARM-1 • pour the fuel drum currently being held by ARM-1 • Behaviors must be selected and executed • selection by name • selection by “contention”

  11. Behavior Structure Definition (defstruct (behavior (:print-function print-behavior)) name test action) (defun print-behavior (self stream indent) (declare (ignore indent)) (format stream "{B ~a}" (behavior-name self))) (defvar *behaviors*) (defun define-behavior (&key name test action) (setf *behaviors* (add-to-end (make-behavior :name name :test test :action action) *behaviors*)))

  12. Definition of add-to-end

  13. Choosing and Executing Behavior (defun find-behavior (name) (find name *behaviors* :key 'behavior-name)) (defun choose-behavior (percept) (first (remove-if-not #'(lambda (b) (funcall (behavior-test b) percept)) *behaviors*))) (defun execute-behavior (b percept) (funcall (behavior-action b) percept))

  14. Defining Behaviors • We now know that a behavior is a test and an action, both functions of a percept. • What are reasonable behaviors for the collection world? • Must depend only on the current percept • Goal is to have them as “low level” as possible while still having them “functional” • recycle all garbage and glass in the world • recycle the piece of glass at position 3, using ARM-1 and the recycler at position 4 • pick up the object at position 3 using ARM-2 • move ARM-2 to position 3

  15. Behavior definitions to accomplish our goals • Recycle all glass, garbage, and empty fuel drums • recycle objects when you have them and there is an appropriate recycler at hand • move from place to place • refuel when necessary

  16. Behavior for picking up a recyclable (define-behavior :name 'pickup-recyclable :test #'(lambda (percept) (and (find-empty-position percept 'BAY-1) (find-object percept '(glass garbage) :OUTSIDE))) :action #'(lambda (percept) (let ((bay-position (find-empty-position percept 'BAY-1)) (obj-position (find-object percept '(glass garbage) :OUTSIDE))) (execute-macrop `(pickup-from-outside ARM-1 ,obj-position)) (execute-macrop `(put-in-bay ARM-1 BAY-1 ,bay-position)))))

  17. Behavior for recycling an object (define-behavior :name 'recycle-object :test #'(lambda (percept) (some #'(lambda (kind) (and (find-object percept kind 'BAY-1) (find-object percept (recycler-for kind) :OUTSIDE))) (kinds-to-recycle))) :action #'(lambda (percept) (do ((kinds (kinds-to-recycle) (cdr kinds)) (done NIL)) (done) (let ((obj-position (find-object percept (car kinds) 'BAY-1)) (recycler-position (find-object percept (recycler-for (car kinds)) :OUTSIDE))) (when (and obj-position recycler-position) (execute-macrop `(pickup-from-bay ARM-1 BAY-1 ,obj-position)) (execute-macrop `(put-inside ARM-1 ,recycler-position)) (setf done T))))))

  18. Summary of behaviors • A behavior is a test and an action • both of functions (only) of the current percept • Behaviors are defined and placed on a global ordered list • Retrieval is either by name, or the first whose test is true given the current percept • Behaviors take action by executing macro-actions (macrops)

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