尝试编写解决此问题的程序：
“您得到了两个水罐，一个5加仑的水罐和一个3加仑的水罐。两个都没有 上面有任何测量标记。有一个水龙头可以用来填充 壶用水。目的是要获得恰好4加仑的水。” 这是我目前拥有的代码：
%(WaterInThree, WaterInFive)
s(A,B).
initial(s(0,0)).
goal(s(A,B)):- A + B =:= 4.
valid(A,B) :- A =< 3, A >=0, B =< 5, B >= 0.
changeState(s(0,B),s(3,B)).
changeState(s(A,0),s(A,5)).
changeState(s(A,B),s(A,0)) :- B > 0, valid(A,B).
changeState(s(A,B),s(0,B)) :- A > 0, valid(A,B).
changeState(s(A,B),s(C,D)) :- B =< 2, D is A + B, C is B - A, valid(C,D).
changeState(s(A,B),s(C,D)) :- B > 2, D is B + ( (5 - A) mod 5), valid(C,D).
changeState(s(A,B),s(3,D)) :- B =< 3, D is B - (3 - A), valid(A,D).
changeState(s(A,B),s(C,D)) :- B =:= 5, C is A + B, D is A - B, valid(C,D).
traverse(StartNode,Sol,_) :- goal(StartNode), Sol = [StartNode].
traverse(StartNode,Sol,Visit) :- changeState(StartNode, NextNode),
not(member(NextNode, Visit)),
traverse(NextNode, PartialSol, [NextNode|Visit]),
Sol = [StartNode | PartialSol].
执行此代码时，出现以下错误：
ERROR: Arguments are not sufficiently instantiated
ERROR: In:
ERROR: [13] _11226=<3
ERROR: [12] valid(_11252,5+(5-3))
ERROR: [11] changeState(s(3,5),s(_11302,5+ ...))
ERROR: [10] traverse(s(3,5),_11336,[s(3,5),...|...])
ERROR: [9] traverse(s(3,0),_11388,[s(3,0),...])
ERROR: [8] traverse(s(0,0),_11440,[s(0,0)])
ERROR: [7] <user>
不太清楚问题出在什么地方，我已经连续数小时试图解决此问题，无法弄清楚出了什么问题。由于这个原因，我什至无法正确测试我创建的changeState谓词是否可以正常工作，因此非常令人沮丧。不胜感激！
编辑，我将其范围缩小到导致错误的这一行：
changeState(s(A,B),s(C,D)) :- B > 2, D is B + ( (5 - A) mod 5), valid(C,D).
虽然真的看不到这将如何导致该错误。
答案 0 :(得分：1)
真的看不出来
changeState(s(A,B),s(C,D)) :- B > 2, D is B + ( (5 - A) mod 5), valid(C,D).
虽然会导致该错误。
_10148=<3
ERROR: Arguments are not sufficiently instantiated
对于
changeState(s(A,B),s(C,D)) :-
B > 2,
D is B + ( (5 - A) mod 5),
valid(C,D).
执行此查询（称为）时
changeState(s(0, 5), X)
A is bound to 0
B is bound to 5
X is bound to s(C,D)
然后
B > 2
查询是
5 > 2
是真的
然后
D is B + ( (5 - A) mod 5)
查询是
D is 5 + ( (5 - 0) mod 5)
D is bound to 5
然后
valid(C,D)
C is unbound
D is bound to 5
查询是
valid (<unbound>,5)
唯一匹配的谓词是
valid(A,B) :- A =< 3, A >=0, B =< 5, B >= 0.
A is unbound
B is bound to 5
然后
A =< 3
由于A是未绑定的，因此比较=<会导致错误，因为它需要绑定两个变量。
回到这句话
changeState(s(A,B),s(C,D)) :- B > 2, D is B + ( (5 - A) mod 5), valid(C,D).
您需要将C绑定到一个值。
如果您使用以下方式设置跟踪
?- visible(+all),leash(-all).
然后启用跟踪
?- trace.
运行查询，您将得到
?- traverse(s(0,0), Sol, [s(0,0)]).
Call: (8) traverse(s(0, 0), _9866, [s(0, 0)])
Unify: (8) traverse(s(0, 0), _9866, [s(0, 0)])
Call: (9) goal(s(0, 0))
Unify: (9) goal(s(0, 0))
Call: (10) 0+0=:=4
Fail: (10) 0+0=:=4
Fail: (9) goal(s(0, 0))
Redo: (8) traverse(s(0, 0), _9866, [s(0, 0)])
Unify: (8) traverse(s(0, 0), _9866, [s(0, 0)])
Call: (9) changeState(s(0, 0), _10092)
Unify: (9) changeState(s(0, 0), s(3, 0))
Exit: (9) changeState(s(0, 0), s(3, 0))
^ Call: (9) not(member(s(3, 0), [s(0, 0)]))
^ Unify: (9) not(user:member(s(3, 0), [s(0, 0)]))
^ Exit: (9) not(user:member(s(3, 0), [s(0, 0)]))
Call: (9) traverse(s(3, 0), _10116, [s(3, 0), s(0, 0)])
Unify: (9) traverse(s(3, 0), _10116, [s(3, 0), s(0, 0)])
Call: (10) goal(s(3, 0))
Unify: (10) goal(s(3, 0))
Call: (11) 3+0=:=4
Fail: (11) 3+0=:=4
Fail: (10) goal(s(3, 0))
Redo: (9) traverse(s(3, 0), _10116, [s(3, 0), s(0, 0)])
Unify: (9) traverse(s(3, 0), _10116, [s(3, 0), s(0, 0)])
Call: (10) changeState(s(3, 0), _10116)
Unify: (10) changeState(s(3, 0), s(3, 5))
Exit: (10) changeState(s(3, 0), s(3, 5))
^ Call: (10) not(member(s(3, 5), [s(3, 0), s(0, 0)]))
^ Unify: (10) not(user:member(s(3, 5), [s(3, 0), s(0, 0)]))
^ Exit: (10) not(user:member(s(3, 5), [s(3, 0), s(0, 0)]))
Call: (10) traverse(s(3, 5), _10140, [s(3, 5), s(3, 0), s(0, 0)])
Unify: (10) traverse(s(3, 5), _10140, [s(3, 5), s(3, 0), s(0, 0)])
Call: (11) goal(s(3, 5))
Unify: (11) goal(s(3, 5))
Call: (12) 3+5=:=4
Fail: (12) 3+5=:=4
Fail: (11) goal(s(3, 5))
Redo: (10) traverse(s(3, 5), _10140, [s(3, 5), s(3, 0), s(0, 0)])
Unify: (10) traverse(s(3, 5), _10140, [s(3, 5), s(3, 0), s(0, 0)])
Call: (11) changeState(s(3, 5), _10140)
Unify: (11) changeState(s(3, 5), s(3, 0))
Call: (12) 5>0
Exit: (12) 5>0
Call: (12) valid(3, 5)
Unify: (12) valid(3, 5)
Call: (13) 3=<3
Exit: (13) 3=<3
Call: (13) 3>=0
Exit: (13) 3>=0
Call: (13) 5=<5
Exit: (13) 5=<5
Call: (13) 5>=0
Exit: (13) 5>=0
Exit: (12) valid(3, 5)
Exit: (11) changeState(s(3, 5), s(3, 0))
^ Call: (11) not(member(s(3, 0), [s(3, 5), s(3, 0), s(0, 0)]))
^ Unify: (11) not(user:member(s(3, 0), [s(3, 5), s(3, 0), s(0, 0)]))
^ Fail: (11) not(user:member(s(3, 0), [s(3, 5), s(3, 0), s(0, 0)]))
Redo: (11) changeState(s(3, 5), _10140)
Unify: (11) changeState(s(3, 5), s(0, 5))
Call: (12) 3>0
Exit: (12) 3>0
Call: (12) valid(3, 5)
Unify: (12) valid(3, 5)
Call: (13) 3=<3
Exit: (13) 3=<3
Call: (13) 3>=0
Exit: (13) 3>=0
Call: (13) 5=<5
Exit: (13) 5=<5
Call: (13) 5>=0
Exit: (13) 5>=0
Exit: (12) valid(3, 5)
Exit: (11) changeState(s(3, 5), s(0, 5))
^ Call: (11) not(member(s(0, 5), [s(3, 5), s(3, 0), s(0, 0)]))
^ Unify: (11) not(user:member(s(0, 5), [s(3, 5), s(3, 0), s(0, 0)]))
^ Exit: (11) not(user:member(s(0, 5), [s(3, 5), s(3, 0), s(0, 0)]))
Call: (11) traverse(s(0, 5), _10164, [s(0, 5), s(3, 5), s(3, 0), s(0, 0)])
Unify: (11) traverse(s(0, 5), _10164, [s(0, 5), s(3, 5), s(3, 0), s(0, 0)])
Call: (12) goal(s(0, 5))
Unify: (12) goal(s(0, 5))
Call: (13) 0+5=:=4
Fail: (13) 0+5=:=4
Fail: (12) goal(s(0, 5))
Redo: (11) traverse(s(0, 5), _10164, [s(0, 5), s(3, 5), s(3, 0), s(0, 0)])
Unify: (11) traverse(s(0, 5), _10164, [s(0, 5), s(3, 5), s(3, 0), s(0, 0)])
Call: (12) changeState(s(0, 5), _10164)
Unify: (12) changeState(s(0, 5), s(3, 5))
Exit: (12) changeState(s(0, 5), s(3, 5))
^ Call: (12) not(member(s(3, 5), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
^ Unify: (12) not(user:member(s(3, 5), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
^ Fail: (12) not(user:member(s(3, 5), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
Redo: (12) changeState(s(0, 5), _10164)
Unify: (12) changeState(s(0, 5), s(0, 0))
Call: (13) 5>0
Exit: (13) 5>0
Call: (13) valid(0, 5)
Unify: (13) valid(0, 5)
Call: (14) 0=<3
Exit: (14) 0=<3
Call: (14) 0>=0
Exit: (14) 0>=0
Call: (14) 5=<5
Exit: (14) 5=<5
Call: (14) 5>=0
Exit: (14) 5>=0
Exit: (13) valid(0, 5)
Exit: (12) changeState(s(0, 5), s(0, 0))
^ Call: (12) not(member(s(0, 0), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
^ Unify: (12) not(user:member(s(0, 0), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
^ Fail: (12) not(user:member(s(0, 0), [s(0, 5), s(3, 5), s(3, 0), s(0, 0)]))
Redo: (12) changeState(s(0, 5), _10164)
Unify: (12) changeState(s(0, 5), s(0, 5))
Call: (13) 0>0
Fail: (13) 0>0
Redo: (12) changeState(s(0, 5), _10164)
Unify: (12) changeState(s(0, 5), s(_10148, _10150))
Call: (13) 5=<2
Fail: (13) 5=<2
Redo: (12) changeState(s(0, 5), _10164)
Unify: (12) changeState(s(0, 5), s(_10148, _10150))
Call: (13) 5>2
Exit: (13) 5>2
Call: (13) _10150 is 5+(5-0)mod 5
Exit: (13) 5 is 5+(5-0)mod 5
Call: (13) valid(_10148, 5)
Unify: (13) valid(_10148, 5)
Call: (14) _10148=<3
ERROR: Arguments are not sufficiently instantiated
ERROR: In:
ERROR: [14] _11032=<3
ERROR: [13] valid(_11058,5) at *.pl:10
ERROR: [12] changeState(s(0,5),s(_11096,5)) at *.pl:17
ERROR: [11] traverse(s(0,5),_11124,[s(0,5),...|...]) at *.pl:26
ERROR: [10] traverse(s(3,5),_11176,[s(3,5),...|...]) at *.pl:28
ERROR: [9] traverse(s(3,0),_11228,[s(3,0),...]) at *.pl:28
ERROR: [8] traverse(s(0,0),_11280,[s(0,0)]) at *.pl:28
ERROR: [7] <user>
Exception: (14) _10148=<3 ? Unknown option (h for help)