Here - Agents Lab - University of Nottingham

1 init module {2 knowledge{3 block(X) :- on(X,_).4 clear(X) :- block(X), not( on(_,X)).5 clear(table).6 }7 actionspec{8 move(X,Y) {9 pre{ clear(X), clear(Y), on(X,Z), not(on(X,Y)) }10 post{ not(on(X,Z)), on(X,Y) }11 }12 }13 goals{ on(b1,table), on(b2,b1), on(b3,b2), on(b4,b3). }14 beliefs{}15 }16 event module { program {17 forall bel(percept(on(X,Y)), not(on(X,Y))) do insert(on(X,Y)).18 forall bel(on(X,Y), not(percept(on(X,Y)))) do delete(on(X,Y)).19 }}20 main module { program[order=random] {21 if bel(true) then move(X,Y).22 }}Fig. 1: A simple Goal agent for solving the Blocks World problemas the desired configuration. The task for the agent is to move blocks aroundone at a time until the final configuration is realised.The program processes percepts and randomly selects an action that is enabledin the Blocks World environment. The init module consists of code toinitialize the mental state of the agent and a single action specification for themove(X,Y) action that the agent can perform in the Blocks World. The Prologrules in the knowledge section of this module define the concepts of a blockand a block being clear. An initial goal is specified in the goals section. Initiallythe agent has no beliefs; the agent must first perceive the environment toobtain information about the blocks’ configuration. The event module is executedat the start of each decision or reasoning cycle of an agent. Its purposeis to process received percepts (and messages). The two forall rules part ofthis module process the percepts received at the start of the cycle of the formpercept(on(X,Y)). The first rule checks whether the agent sees that a block Xis on top of a block Y and inserts this fact if the agent does not currently believeit; the second rule removes facts that are believed but not perceived (assumingfull observability this is a sound rule).The main module consists of the decision logic for acting in the environmentand selects actions after the mental state has been updated with the most recentperceptual information. The option order=random associated with the program154