Wolf goat cabbage

Description

Solving the wolf, goat, and cabbage problem

Source: The Art of Prolog

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Program source code: wolf_goat_cabbage.pl

Listing

/*
   States for the wolf, goat and cabbage problem are a structure
   wgc(Boat,Left,Right), where Boat is the bank on which the boat 
   currently is, Left is the list of occupants on the left bank of 
   the river, and Right is the list of occupants on the right bank.
*/
     initial_state(wgc,wgc(left,[wolf,goat,cabbage],[])).
 
     final_state(wgc(right,[],[wolf,goat,cabbage])).
 
     move(wgc(left,L,R),Cargo) :- member(Cargo,L).
     move(wgc(right,L,R),Cargo) :- member(Cargo,R).
     move(wgc(B,L,R),alone).
 
     update(wgc(B,L,R),Cargo,wgc(B1,L1,R1)) :-
         update_boat(B,B1), update_banks(Cargo,B,L,R,L1,R1).
 
     update_boat(left,right).        
     update_boat(right,left).
 
     update_banks(alone,B,L,R,L,R).
     update_banks(Cargo,left,L,R,L1,R1) :- 
	select(Cargo,L,L1), insert(Cargo,R,R1).
     update_banks(Cargo,right,L,R,L1,R1) :- 
	select(Cargo,R,R1), insert(Cargo,L,L1).
 
     insert(X,[Y|Ys],[X,Y|Ys]) :-
	precedes(X,Y).
     insert(X,[Y|Ys],[Y|Zs]) :-
	precedes(Y,X), insert(X,Ys,Zs).
     insert(X,[],[X]).
 
     precedes(wolf,X).
     precedes(X,cabbage).
 
     legal(wgc(left,L,R)) :- not(illegal(R)).
     legal(wgc(right,L,R)) :- not(illegal(L)).
 
	illegal(Bank) :- member(wolf,Bank), member(goat,Bank).
        illegal(Bank) :- member(goat,Bank), member(cabbage,Bank).
 
	select(X,[X|Xs],Xs).
	select(X,[Y|Ys],[Y|Zs]) :-
		select(X,Ys,Zs).
 
%    Program 20.2:  Solving the wolf, goat, and cabbage problem

Comments

pl/prolog/pllib/wolf_goat_cabbage.txt · ostatnio zmienione: 2017/07/17 08:08 (edycja zewnętrzna)
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