%% s_blocks2.sp -- SPARC version of blocks2.lp from Chapter 8, Section 8.1
%% Last Modified: 2/21/2014
%% FOR EXPERIMENTATION ONLY
%% Description of a basic block world domain but with defined 
%% fluent above. Demonstrates problem that necessitates two types of
%% fluents -- inertial and defined. 
%% 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.

#const n = 2.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
sorts
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

#block = [b][0..7].

#location = #block + {t}.

#fluent = on(#block(X),#location(Y)):X!=Y +
          above(#block(X),#location(Y)):X!=Y.
          
#action = put(#block(X),#location(Y)):X!=Y.

#step = 0..n.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
predicates
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

holds(#fluent,#step).
occurs(#action,#step).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
rules
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% 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) :- 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).

%% A block cannot be in two locations at once:
-holds(on(B,L2),I) :- holds(on(B,L1),I),    
                      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),     
                      B1 != B2.
                   
% Inertia:   
holds(F,I+1) :- holds(F,I),                  
                not -holds(F,I+1).

-holds(F,I+1) :- -holds(F,I),                
                 not holds(F,I+1).
   
                 
%% It is impossible to move an occupied block:
-occurs(put(B,L),I) :-  holds(on(B1,B),I).     

%% It is impossible to move a block onto an occupied block:
-occurs(put(B1,B),I) :-  #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).

%% Block B is located above location L:

holds(above(B,L),I) :- holds(on(B,L),I).
holds(above(B,L),I) :- holds(on(B,B1),I),
                       holds(above(B1,L),I).
%% CWA for above:
-holds(above(B,L),I) :- not holds(above(B,L),I). 
                          
%% The statement that illustrates the problem:
:- -holds(above(b2,b0),1).