动态修改全局数据
asserta(X) :把子句X当作此子句的谓词的第一个子句加入到动态数据库中，不可回溯。
assert(X)或assertz(X) :把子句X当作此子句的谓词的最后一个子句加入到动态数据库中，不可回溯。
retract(X) :把子句X从动态数据库中删除，不可回溯。
%swipl -s room.pl
%Hansen
:-dynamic here/1.
:-dynamic location/2.
:-dynamic bag/1.
%房间定义
room(kitchen).
room(office).
room(hall).
room(diningroom).
room(cellar).
%门定义
door(office, hall).
door(kitchen, office).
door(hall, diningroom).
door(kitchen, cellar).
door(diningroom, kitchen).
%规则：有门的两个房间是相通的
connect(X,Y) :- door(X,Y).
connect(X,Y) :- door(Y,X).
%物品在哪个房间
location(desk, office).
location(apple, kitchen).
location(flashlight, desk).
location(washingmachine, cellar).
location(nani, washingmachine).
location(broccoli, kitchen).
location(crackers, kitchen).
location(computer, office).
%背包
bag(tourch).
%哪些物品可以吃
edible(apple).
edible(crackers).
edible(broccoli).
%当前位置
here(hall).
%移动
move(Place):- can_go(Place),retract(here(X)), asserta(here(Place)).
can_go(Place):- here(X), connect(X, Place).
can_go(Place):- write('You can''t go to '),write(Place),write(' from here.'), nl, fail.
%获取物品
take(X):- can_take(X), retract(location(X,_)), asserta(bag(X)), write(X), write(' taken.'), nl.
can_take(Thing):- here(Place), location(Thing, Place).
can_take(Thing):- write('There is no '), write(Thing), write(' here.'), nl, fail.
%放下物品
put(X):- can_put(X), here(Place), retract(bag(X)), asserta(location(X,Place)), write(X), write(' put.'), nl.
can_put(Thing):- bag(Thing).
can_put(Thing):- write('There is no '), write(Thing), write(' in your bag.'), nl, fail.
%房间物品列表
list_things(Place):- location(X, Place),tab(2),write(X),nl,fail.
list_things(_).
%相连的
list_connections(Place):- connect(Place, X),tab(2),write(X),nl,fail.
list_connections(_).
%持有物品列表
list_bag(Thing):- bag(X),tab(2),write(X),nl,fail.
list_bag(_).
%吃东西
eat(Thing):- can_eat(Thing), retract(bag(X)), write(Thing), write(' eaten. Yummy!').
can_eat(Thing):- bag(Thing), edible(Thing).
can_eat(Thing):- not(bag(Thing)), write('There is no '), write(Thing), write(' in your bag.'), nl, fail.
can_eat(Thing):- bag(Thing), write('You can''t eat the '), write(Thing), write('.'), nl, fail.
%查看房间情况
look :-
here(Place), write('You are in the '), write(Place), nl,
write('You can see:'),nl,list_things(Place),
write('You can go to:'), nl, list_connections(Place),
write('You have:'),nl,list_bag(Thing).
%帮助
game :-
write('Look around: look/0'),nl,
write('Move around: move/1'),nl,
write('Take something: take/1'),nl,
write('Eat something: eat/1').
1 ?- game. Look around: look/0 Move around: move/1 Take something: take/1 Eat something: eat/1 true. 2 ?- look. You are in the hall You can see: You can go to: diningroom office You have: tourch true. 3 ?- move(diningroom). true . 4 ?- look. You are in the diningroom You can see: You can go to: kitchen hall You have: tourch true. 5 ?- move(kitchen). true . 6 ?- look. You are in the kitchen You can see: apple broccoli crackers You can go to: office cellar diningroom You have: tourch true. 7 ?- take(apple). apple taken. true . 8 ?- look. You are in the kitchen You can see: broccoli crackers You can go to: office cellar diningroom You have: apple tourch true. 9 ?- eat(apple). apple eaten. Yummy! true .