%% blocks1.lp -- Chapter 8, Section 8.1 %% Last Modified: 2/1/2014 %% First attempt at a description of a basic block world domain. %% This program is meant to be experimented with in conjunction with %% the text. See blocks3.lp for the finished version. %% %% 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. %% blocks: block(b0). block(b1). block(b2). block(b3). block(b4). block(b5). block(b6). block(b7). %% A location can be a block or the table. location(X) :- block(X). location(t). #const n = 2. step(0..n). %% "Block B is on location L" is a property that changes %% with time. fluent(on(B,L)) :- block(B), location(L). %% "Put block B on location L" is a possible action in our %% domain provided we don't try to put a block onto itself. action(put(B,L)) :- block(B), location(L), B != L. %% holds(on(B,L),I): a block B is on location L at step I. %% This is a particular intial configuration. %% It can be changed at will: 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). %% Putting block B on location L at step I %% causes B to be on L at step I+1: holds(on(B,L),I+1) :- occurs(put(B,L),I), I < n. %% A block cannot be in two locations at once: -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: -holds(on(B2,B),I) :- block(B), holds(on(B1,B),I), block(B2), B1 != B2. % Inertia: holds(F,I+1) :- holds(F,I), not -holds(F,I+1), I < n. -holds(F,I+1) :- -holds(F,I), not holds(F,I+1), I < n. %% It is impossible to move an occupied block: -occurs(put(B,L),I) :- location(L), holds(on(B1,B),I). %% It is impossible to move a block onto an occupied block: -occurs(put(B1,B),I) :- block(B1), block(B), holds(on(B2,B),I). %% Specific actions for testing. %% Change these at will: occurs(put(b2,t),0). occurs(put(b7,b2),1). %#show holds/2.