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Monkey and banana in thinking as a calculation

I read the book “Thinking Like Computing” and wrote the code as chapter 9.4:

plan(L) :-
   initial_state(I),
   goal_state(G),
   reachable(I, L, G).

initial_state([]).

legal_move(S, A, [A | S]) :-
    poss(A, S).

goal_state(S) :-
    has_bananas(S).

reachable(S, [], S).
reachable(S1, [M | L], S3) :-
    legal_move(S1, M, S2),
    reachable(S2, L, S3).

location(box, loc3, []).
location(box, L, [push(L) | _]).
location(box, L, [A | S]) :-
    \+ A = push(L),
    location(box, L, S).
location(bananas, loc1, _).
location(monkey, loc2, []).
location(monkey, L, [push(L) | _]).
location(monkey, L, [go(L) | _]).
location(monkey, L, [climb_off | S]) :-
    location(monkey, L, S).
location(monkey, L, [A | S]) :-
    \+ A = push(_), \+ A = go(_), location(monkey, L, S).

on_box([climb_on | _]).
on_box([A | S]) :- \+ A = climb_off, on_box(S).

has_bananas([grab | S]) .
has_bananas([_ | S]) :- has_bananas(S).

poss(climb_off, S) :- on_box(S).
poss(go(_), S) :- \+ on_box(S).
poss(grab, S) :-
    on_box(S), location(box, L, S), location(bananas, L, S).

poss(push(_), S) :- poss(climb_on, S).
poss(climb_on, S) :-
    \+ on_box(S), location(box, L, S), location(monkey, L, S).

But I found that the program never stops ... After printing the stack information, I found that it goal_stategenerated lists of infinite length. I tried to limit the length of the lists inhas_banana

has_bananas([grab | S], N) :- length(S, NS), NS is N - 1.
has_bananas([_ | S], N) :- \+ N = 0, has_bananas(S, N - 1).

which Nrefers to the length Lin plan(L)(for example, Nequal to 4 when requested plan([M1, M2, M3, M4])). But that does not work.

Is there any solution?

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1 answer

Non-term - Prolog, , , . . Prolog.

. . , , . , false . ? , : . , , . , . , :

?- length(L, 4), plan(L).

, . 1.

, false. , .

:

?- length(L, 4), plan(L).

plan(L) :-
   initial_state(I),
   goal_state(G), false,
   reachable(I, L, G).

initial_state([]).

goal_state(S) :-
   has_bananas(S), false.

has_bananas([grab | S]) :- false.
has_bananas([_ | S]) :-
   has_bananas(S), false.

( failure-slice) . , - . , .

, :

plan(L) :-
   initial_state(I),
   reachable(I, L, G),
   goal_state(G).

1) , .

+3

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