%PR3 Solution Guide:

% total: 20 points


%Ex3.1 [B]  4 points (2+2)  
% conc is descrived in section 3.2.2.  It is often called "append"
conc( [],L,L).
conc( [X|L1], L2, [X|L3]) :- conc(  L1,L2,L3).

% part(a). del3 deletes the last three items from L, producing L1.
del3(L,L1) :- conc(L1,[_,_,_],L).

%part(b) del3twice deletes the first three and the last three items from L.
del3twice(L,L1) :- del3(L,L2), conc([_,_,_],L1,L2).

%Ex3.2 [B]  4 points (2+2)
% Ex3.2 p.67
% last1(Item,List) holds if Item is the last item in List; it uses conc
last1(Item,List) :- conc(_,[Item],List).
% conc is descrived in section 3.2.2.  It is often called "append"
%conc( [],L,L).
%conc( [X|L1], L2, [X|L3]) :- conc(  L1,L2,L3).

% last2(Item,List) holds if Item is the last item in List; it does not use conc
last2(Item,[Item]).
last2(Item, [_|L]) :- last2(Item,L).

%Ex3.4 [B]  3 points
% Naive Reverse.  rev(X,Y) if list X is the reverse of list Y.
rev( [],[]).
rev( [X|Y], Z) :- rev( Y,W), conc( W,[X],Z). % See above for conc

%Ex3.10 [B] 4 points for either solution

%canget(X,Y) if monkey can get banana from state X by doing actions in Y
canget( state(_,_,_,has), [ ]).
canget( State, [Action|Actions]) :-
  move( State, Action, NewState),
  canget( NewState, Actions).

%canget(X,Y,Z) if monkey can get banana from state X by doing actions
% in Z-Y, in reverse order
canget1( state(_,_,_,has), Actions, Actions).
canget1( State1, Actions, Path)  :- 
  move( State1, Move, State2),
  canget1( State2, [Move | Actions], Path).

% Find the operator declarations: 5 points