Question

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。

Answer 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)

参数没有足够实例化的序言

1 个答案: