%% bw.lp -- Chapter 8, Section 8.5.2 %% Last Modified: 2/4/14 %% Blocks world domain from AL description %% %% The basic blocks world consists of a robotic arm that can manipulate %% configurations of same-sized cubic blocks on a table. There are %% limitations to what the robotic arm can do. It can move %% unoccupied blocks, one at a time, onto other unoccupied blocks or %% onto the table. (An unoccupied block is one that does not have another %% block stacked on it.) At any given step, a block can be in at most %% one location; in other words, a block can be directly on top of one %% other block, or on the table. We do not impose a limit on how tall %% our towers can be. Our table is big enough to hold all the blocks, %% even if they are not stacked. We do not take into account spatial %% relationships of towers, just which blocks are on top %% of each other and which blocks are on the table. block(b0). block(b1). block(b2). block(b3). block(b4). block(b5). block(b6). block(b7). location(X) :- block(X). location(t). #const n = 1. step(0..n). %% Fluents %% fluent(inertial, on(B,L)) :- block(B), location(L). fluent(defined, above(B,L)) :- block(B), location(L). %% Actions %% action(put(B,L)) :- block(B), location(L), B != L. %% Laws %% %% Putting block B on location L at step I %% causes B to be on L at step I+1: %% put(B,L) causes on(B,L) holds(on(B,L),I+1) :- occurs(put(B,L),I), I < n. %% A block cannot be in two locations at once: %% -on(B,L2) if on(B,L1), L1 != L2 -holds(on(B,L2),I) :- holds(on(B,L1),I), location(L2), L1 != L2. %% Only one block can be set directly on top of another: %% -on(B2,B) if on(B1,B), B1 != B2 -holds(on(B2,B),I) :- holds(on(B1,B),I), block(B), block(B2), B1 != B2. %% B is above L if it is directly on top of it or on top of %% another block that is above L: %% above(B,L) if on (B,L) %% above(B,L) if on(B,B1), above(B1,L) holds(above(B2,B1),I) :- holds(on(B2,B1),I). holds(above(B2,B1),I) :- holds(on(B2,B),I), holds(above(B,B1),I). %% It is impossible to move an occupied block: %% impossible put(B,L) if on (B1,B) -occurs(put(B,L),I) :- location(L), holds(on(B1,B),I). %% It is impossible to move a block onto an occupied block: %% impossible put(B1,B) if on(B2,B). -occurs(put(B1,B),I) :- block(B1), block(B), holds(on(B2,B),I). %% CWA for Defined Fluents -holds(F,I) :- fluent(defined,F), step(I), not holds(F,I). %% General Inertia Axiom holds(F,I+1) :- fluent(inertial,F), holds(F,I), not -holds(F,I+1), I < n. -holds(F,I+1) :- fluent(inertial,F), -holds(F,I), not holds(F,I+1), I < n. %% CWA for Actions -occurs(A,I) :- action(A), step(I), not occurs(A,I). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% Specific initial situation. %% Change at will: %% holds(on(B,L),I): a block B is on location L at step I. %holds(on(b0,t),0). %holds(on(b3,b0),0). %holds(on(b2,b3),0). %holds(on(b1,t),0). %holds(on(b4,b1),0). %holds(on(b5,t),0). %holds(on(b6,b5),0). %holds(on(b7,b6),0). %% If block B is not known to be on location L at step 0, %% then we assume it is not. %-holds(on(B,L),0) :- block(B), location(L), % not holds(on(B,L),0). %% Particular action -- put b2 on the table at step 0 %% Change at will: %occurs(put(b2,t),0).