底部的程序应该返回目标缺少的子句，在这种情况下p(1, 3, fire)可证明的。
问题是它返回一个解决方案"太多"，如此输出中的最后一个解决方案所示：
?- main.
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,2,johnDroppedAMatch)
true ;
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,1,johnWasTired)
true ;
MISSING PREMISES:
precedes(3,3)
p(A,3,presenceOfFlammableMaterial)
p(B,2,johnWasTired)
true ;
false.
我想要的只是：
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,2,johnDroppedAMatch)
true ;
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,1,johnWasTired)
true ;
我很难理解出了什么问题，并希望得到一些改进它的提示：-(，或者一些文学提示(我已经熟悉马库斯·特里斯卡的优秀页面(。
重要的谓词是missing0(G, M)，其中G是一个目标，M缺少子句的列表。我对这个问题的一个怀疑是，可能有无限数量的子句失败，所以我错过了某种"停止"条件。
我在SWI Prolog论坛上发布了同样的问题，但没有得到任何回应。我正在运行SWI Prolog。
% https://www.swi-prolog.org/pldoc/doc/_SWI_/library/clp/clpr.pl
:-use_module(library(clpr)).
% time is ordered
precedes(1, 2).
precedes(2, 3).
% knowledge
p(X1, T2, johnDroppedAMatch):-
p(X2, T1, johnWasTired),
precedes(T1, T2),
{X1 = 0.5 * X2}.
p(X1, T2, fire):-
p(X2, T1, presenceOfFlammableMaterial),
p(X3, T1, johnDroppedAMatch),
precedes(T1, T2),
{X1 = 0.7 * X2 * X3}.
% --- Reasoning about knowledge
missing(G, M) :- call(G),
M = ['There are no missing premises.'].
missing(G, M) :- +clause(G, _),
M = ['There are no clauses for the goal.'].
missing(G, M) :- clause(G, B), +G, missing0(B, M).
% -- Look for missing clauses in a conjunction
missing0(G, M) :- G = (G1, G2), !,
missing0(G1, M1), missing0(G2, M2), append(M1, M2, M).
% -- Look for missing clauses in a disjunction
missing0(G, M) :- G = (G1; _), missing0(G1, M).
% -- Look for missing clauses in a disjunction
missing0(G, M) :- G = (_; G2), missing0(G2, M).
% -- If G is callable then it is not missing
missing0(G, M) :- call(G), M = [].
% G fails, and is neither a conjunction nor a disjunction, so
% put in in M. Here I collect missing clauses.
missing0(G, M) :- +G, G = (_, _), G = (_; _), M = [G].
% If G fails and if B is in the body of G, check what predicates are
% missing for B to be provable. G = {_} is to avoid an error when
% using clause/2 on clpr predicates.
missing0(G, M) :- +G, G = {_}, clause(G, B), missing0(B, M).
showMissing(M) :- copy_term_nat(M, M1),
numbervars(M1, 0, _, [attvar(bind)]),
sort(M1, M2),
nl, writeln('MISSING PREMISES:'),
maplist(writeln, M2).
main :- missing(p(1, 3, fire), M), showMissing(M).
不是答案，但我对代码进行了一些修改，添加了一些打印输出并使其相当确定。它现在报告单个解决方案。
原始代码，略微审查
这是原始代码，带有一些打印输出。它的报告与以前完全相同，输出未排序以便能够跟踪它首先命中的内容。
:-use_module(library(clpr)).
% ======================
% knowledge
% ======================
% time is ordered
% Note: Time is not transitive as precedes(1,3) is missing!
precedes(1, 2).
precedes(2, 3).
p(X1, T2, johnDroppedAMatch):-
p(X2, T1, johnWasTired),
precedes(T1, T2),
{X1 = 0.5 * X2}.
p(X1, T2, fire):-
p(X2, T1, presenceOfFlammableMaterial),
p(X3, T1, johnDroppedAMatch),
precedes(T1, T2),
{X1 = 0.7 * X2 * X3}.
% ======================
% reasoning about knowledge
% ======================
% Note: What exactly does it mean for a premise to be "missing"?
% Are variables to be resolved when reporting?
missing(G, M) :- call(G),
M = ['There are no missing premises.'].
missing(G, M) :- +clause(G, _),
M = ['There are no clauses for the goal.'].
missing(G, M) :- clause(G, B), +G, missingr(B, M, 0).
% --- Recursively look for missing stuff in a goal
% D is the Depth of the analysis
% SP is a string of spaces for indentation
missingr(G, M, D) :- G = (G1, G2), !,
sp(D,SP), format("~w«~w» AND «~w»n",[SP,G1,G2]), spinc(D,DP),
missingr(G1, M1, DP),
missingr(G2, M2, DP),
append(M1, M2, M).
missingr(G, M, D) :- G = (G1; _), !,
sp(D,SP), format("~w«~w» OR «~w»n",[SP,G1,"..."]), spinc(D,DP),
missingr(G1, M, DP).
missingr(G, M, D) :- G = (_ ; G2), !,
sp(D,SP), format("~w«~w» OR «~w»n",[SP,"...",G2]), spinc(D,DP),
missingr(G2, M, DP).
missingr(G, M, D) :- sp(D,SP), format("~wMaybe «~w» can be called?n",[SP,G]),
call(G),
format("~w«~w» succeeds; nothing is missing here.n",[SP,G]),
M = [].
missingr(G, M, D) :- +G, G = (_,_), G = (_;_),
sp(D,SP), format("~w«~w» is not provable, not a conjunction, not a disjunction: Consider missing!n",[SP,G]),
M = [G].
missingr(G, M, D) :- +G, G = {_}, clause(G, B),
sp(D,SP), format("~w«~w» is not provable, not a constraint, and a clause with body «~w», continue with bodyn",[SP,G,B]), spinc(D,DP),
missingr(B, M, DP).
% Igniter
showMissing(M) :- copy_term_nat(M, M1),
numbervars(M1, 0, _, [attvar(bind)]),
% sort(M1, M2), % do not sort so that terms are output in found order
M2 = M1,
nl, writeln('MISSING PREMISES:'),
maplist(writeln, M2).
main :- missing(p(1, 3, fire), M), showMissing(M).
% Generate string of N spaces fast.
spinc(In,Out) :- Out is In+2.
sp(0,"") :- !.
sp(1,".") :- !.
sp(Len,Str) :- Len > 1,
Lenx is Len div 2, Remx is Len rem 2,
sp(Lenx,Strx),
string_concat(Strx,Strx,Stry),
(Remx == 0 -> Str = Stry ; string_concat(Stry,".",Str)),!.
输出
?- main.
«p(_7002,_7004,presenceOfFlammableMaterial)» AND «p(_7010,_7004,johnDroppedAMatch),precedes(_7004,3),{1=0.7*_7002*_7010}»
..Maybe «p(_7002,_7004,presenceOfFlammableMaterial)» can be called?
..«p(_7002,_7004,presenceOfFlammableMaterial)» is not provable, not a conjunction, not a disjunction: Consider missing!
..«p(_7010,_7004,johnDroppedAMatch)» AND «precedes(_7004,3),{1=0.7*_7002*_7010}»
....Maybe «p(_7010,_7004,johnDroppedAMatch)» can be called?
....«p(_7010,_7004,johnDroppedAMatch)» is not provable, not a conjunction, not a disjunction: Consider missing!
....«precedes(_7004,3)» AND «{1=0.7*_7002*_7010}»
......Maybe «precedes(_7004,3)» can be called?
......«precedes(2,3)» succeeds; nothing is missing here.
......Maybe «{1=0.7*_7002*_7010}» can be called?
......«{1=0.7*_7914*_7940}» succeeds; nothing is missing here.
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,2,johnDroppedAMatch)
true ;
....«p(_7010,_7004,johnDroppedAMatch)» is not provable, not a constraint, and a clause with body «p(_7278,_7280,johnWasTired),precedes(_7280,_7004),{_7010=0.5*_7278}», continue with body
......«p(_7278,_7280,johnWasTired)» AND «precedes(_7280,_7004),{_7010=0.5*_7278}»
........Maybe «p(_7278,_7280,johnWasTired)» can be called?
........«p(_7278,_7280,johnWasTired)» is not provable, not a conjunction, not a disjunction: Consider missing!
........«precedes(_7280,_7004)» AND «{_7010=0.5*_7278}»
..........Maybe «precedes(_7280,_7004)» can be called?
..........«precedes(1,2)» succeeds; nothing is missing here.
..........Maybe «{_7010=0.5*_7278}» can be called?
..........«{_8266=0.5*_8368}» succeeds; nothing is missing here.
....«precedes(2,3)» AND «{1=0.7*_7002*_8266}»
......Maybe «precedes(2,3)» can be called?
......«precedes(2,3)» succeeds; nothing is missing here.
......Maybe «{1=0.7*_7002*_8266}» can be called?
......«{1=0.7*_9472*_8266}» succeeds; nothing is missing here.
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,1,johnWasTired)
true ;
..........«precedes(2,3)» succeeds; nothing is missing here.
..........Maybe «{_7010=0.5*_7278}» can be called?
..........«{_8266=0.5*_8368}» succeeds; nothing is missing here.
....«precedes(3,3)» AND «{1=0.7*_7002*_8266}»
......Maybe «precedes(3,3)» can be called?
......«precedes(3,3)» is not provable, not a conjunction, not a disjunction: Consider missing!
......Maybe «{1=0.7*_7002*_8266}» can be called?
......«{1=0.7*_9476*_8266}» succeeds; nothing is missing here.
MISSING PREMISES:
p(A,3,presenceOfFlammableMaterial)
p(B,2,johnWasTired)
precedes(3,3)
true ;
false.
考虑到这一点，">缺少谓语">是什么意思就变得不清楚了，甚至在解释过程中遇到合词或析取时应该发生什么。需要更多细节！
修改代码尝试
这是修改后的代码，它似乎符合所需的内容，但更具确定性，仅输出一个解决方案：
:-use_module(library(clpr)).
% ======================
% knowledge
% ======================
% time is ordered
% Note: Time is not transitive as precedes(1,3) is missing!
precedes(1, 2).
precedes(2, 3).
p(X1, T2, johnDroppedAMatch):-
p(X2, T1, johnWasTired),
precedes(T1, T2),
{X1 = 0.5 * X2}.
p(X1, T2, fire):-
p(X2, T1, presenceOfFlammableMaterial),
p(X3, T1, johnDroppedAMatch),
precedes(T1, T2),
{X1 = 0.7 * X2 * X3}.
% ======================
% reasoning about knowledge
% ======================
% Note: What exactly does it mean for a premise to be "missing"?
% Are variables to be resolved when reporting?
missing(G, M) :- call(G),
M = ['There are no missing premises.'].
missing(G, M) :- +clause(G, _),
M = ['There are no clauses for the goal.'].
missing(G, M) :- clause(G, B), +G, missingr(B, M, 0).
% --- Recursively look for missing stuff in a goal
% Conjunction
% In a conjunction we can fail on left or right, go down both branches.
missingr(G, M, D) :- G = (G1, G2), !,
sp(D,SP), format("~w«~w» AND «~w»n",[SP,G1,G2]), spinc(D,DP),
missingr(G1, M1, DP),
missingr(G2, M2, DP),
append(M1, M2, M).
% Disjunction. Finagle a proper guard!
% Note: In a disjunction we fail if we fail on both sides, but then what to report???
missingr(G, M, D) :- G = (G1; G2), !,
sp(D,SP), format("~w«~w» OR «~w»n",[SP,G1,G2]), spinc(D,DP),
(missingr(G1, M, DP) ; missingr(G2, M, DP)).
% If G is callable and succeeds then it is not missing.
% The call will unify variables, which may or may not be what we want.
missingr(G, M, D) :- sp(D,SP), format("~wMaybe «~w» can be called?n",[SP,G]),
call(G), !,
format("~w«~w» succeeds; nothing is missing here.n",[SP,G]),
M = [].
% If G fails and if B is the body of G, check what predicates are
% missing for B to be provable. G = {_} is to avoid an error when
% using clause/2 on clpr predicates.
missingr(G, M, D) :- +G, !,
sp(D,SP), format("~w«~w» is nonprovablen",[SP,G]), spinc(D,DP),
nonprovable(G, M, DP).
nonprovable(G, M, D) :- G = {_}, clause(G, B), !,
sp(D,SP), format("~w«~w» is a nonprovable clause with body «~w», continue with bodyn",[SP,G,B]), spinc(D,DP),
missingr(B, M, DP).
nonprovable(G, M, D) :- G = {_}, !,
sp(D,SP), format("~w«~w» is a nonprovable non-clause: considered missing!n",[SP,G]),
M = [G].
nonprovable(G, M, D) :- sp(D,SP), format("~w«~w» is a constraint; dropped!n",[SP,G]),
M = [].
% Igniter
showMissing(M) :- copy_term_nat(M, M1),
numbervars(M1, 0, _, [attvar(bind)]),
nl, writeln('MISSING PREMISES:'),
maplist(writeln, M1).
main :- missing(p(1, 3, fire), M), showMissing(M).
% Generate string of N spaces fast.
spinc(In,Out) :- Out is In+2.
sp(0,"") :- !.
sp(1,".") :- !.
sp(Len,Str) :- Len > 1,
Lenx is Len div 2, Remx is Len rem 2,
sp(Lenx,Strx),
string_concat(Strx,Strx,Stry),
(Remx == 0 -> Str = Stry ; string_concat(Stry,".",Str)),!.
新输出
运行它会生成单个解决方案：
?- main.
«p(_5182,_5184,presenceOfFlammableMaterial)» AND «p(_5190,_5184,johnDroppedAMatch),precedes(_5184,3),{1=0.7*_5182*_5190}»
..Maybe «p(_5182,_5184,presenceOfFlammableMaterial)» can be called?
..«p(_5182,_5184,presenceOfFlammableMaterial)» is nonprovable
....«p(_5182,_5184,presenceOfFlammableMaterial)» is a nonprovable non-clause: considered missing!
..«p(_5190,_5184,johnDroppedAMatch)» AND «precedes(_5184,3),{1=0.7*_5182*_5190}»
....Maybe «p(_5190,_5184,johnDroppedAMatch)» can be called?
....«p(_5190,_5184,johnDroppedAMatch)» is nonprovable
......«p(_5190,_5184,johnDroppedAMatch)» is a nonprovable clause with body «p(_5572,_5574,johnWasTired),precedes(_5574,_5184),{_5190=0.5*_5572}»,
........«p(_5572,_5574,johnWasTired)» AND «precedes(_5574,_5184),{_5190=0.5*_5572}»
..........Maybe «p(_5572,_5574,johnWasTired)» can be called?
..........«p(_5572,_5574,johnWasTired)» is nonprovable
............«p(_5572,_5574,johnWasTired)» is a nonprovable non-clause: considered missing!
..........«precedes(_5574,_5184)» AND «{_5190=0.5*_5572}»
............Maybe «precedes(_5574,_5184)» can be called?
............«precedes(1,2)» succeeds; nothing is missing here.
............Maybe «{_5190=0.5*_5572}» can be called?
............«{_6626=0.5*_6728}» succeeds; nothing is missing here.
....«precedes(2,3)» AND «{1=0.7*_5182*_6626}»
......Maybe «precedes(2,3)» can be called?
......«precedes(2,3)» succeeds; nothing is missing here.
......Maybe «{1=0.7*_5182*_6626}» can be called?
......«{1=0.7*_7658*_6626}» succeeds; nothing is missing here.
MISSING PREMISES:
p(A,2,presenceOfFlammableMaterial)
p(B,1,johnWasTired)
true.
但如前所述，我们实际上想要在这里拥有什么？