Prolog：句子解析器
我已经坐在这里好几个小时了，只是盯着这段代码，不知道我做错了什么。我通过跟踪代码知道发生了什么（当它遇到 verbPhrase 时，它会进入一个永恒的循环）。任何提示都非常受欢迎。谢谢。
% Knowledge-base
det(the).
det(a).
adjective(quick).
adjective(brown).
adjective(orange).
adjective(sweet).
noun(cat).
noun(mat).
noun(fox).
noun(cucumber).
noun(saw).
noun(mother).
noun(father).
noun(family).
noun(depression).
prep(on).
prep(with).
verb(sat).
verb(nibbled).
verb(ran).
verb(looked).
verb(is).
verb(has).
% Sentece Structures
sentence(Phrase) :-
append(NounPhrase, VerbPhrase, Phrase),
nounPhrase(NounPhrase),
verbPhrase(VerbPhrase).
sentence(Phrase) :-
verbPhrase(Phrase).
nounPhrase([]).
nounPhrase([Head | Tail]) :-
det(Head),
nounPhrase2(Tail).
nounPhrase(Phrase) :-
nounPhrase2(Phrase).
nounPhrase(Phrase) :-
append(NP, PP, Phrase),
nounPhrase(NP),
prepPhrase(PP).
nounPhrase2([]).
nounPhrase2(Word) :-
noun(Word).
nounPhrase2([Head | Tail]) :-
adjective(Head),
nounPhrase2(Tail).
prepPhrase([]).
prepPhrase([Head | Tail]) :-
prep(Head),
nounPhrase(Tail).
verbPhrase([]).
verbPhrase(Word) :-
verb(Word).
verbPhrase([Head | Tail]) :-
verb(Head),
nounPhrase(Tail).
verbPhrase(Phrase) :-
append(VP, PP, Phrase),
verbPhrase(VP),
prepPhrase(PP).
Been sat here for hours now just staring at this code and have no idea what I'm doing wrong. I know what's happening from tracing the code through (it is going on an eternal loop when it hits verbPhrase). Any tips are more then welcome. Thank you.
% Knowledge-base
det(the).
det(a).
adjective(quick).
adjective(brown).
adjective(orange).
adjective(sweet).
noun(cat).
noun(mat).
noun(fox).
noun(cucumber).
noun(saw).
noun(mother).
noun(father).
noun(family).
noun(depression).
prep(on).
prep(with).
verb(sat).
verb(nibbled).
verb(ran).
verb(looked).
verb(is).
verb(has).
% Sentece Structures
sentence(Phrase) :-
append(NounPhrase, VerbPhrase, Phrase),
nounPhrase(NounPhrase),
verbPhrase(VerbPhrase).
sentence(Phrase) :-
verbPhrase(Phrase).
nounPhrase([]).
nounPhrase([Head | Tail]) :-
det(Head),
nounPhrase2(Tail).
nounPhrase(Phrase) :-
nounPhrase2(Phrase).
nounPhrase(Phrase) :-
append(NP, PP, Phrase),
nounPhrase(NP),
prepPhrase(PP).
nounPhrase2([]).
nounPhrase2(Word) :-
noun(Word).
nounPhrase2([Head | Tail]) :-
adjective(Head),
nounPhrase2(Tail).
prepPhrase([]).
prepPhrase([Head | Tail]) :-
prep(Head),
nounPhrase(Tail).
verbPhrase([]).
verbPhrase(Word) :-
verb(Word).
verbPhrase([Head | Tail]) :-
verb(Head),
nounPhrase(Tail).
verbPhrase(Phrase) :-
append(VP, PP, Phrase),
verbPhrase(VP),
prepPhrase(PP).
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经过一番网上搜索后，我现在弄清楚了，所以如果其他人遇到困难，我会在这里回答。
问题是追加创建了一个空列表。该列表作为参数传递，然后再次拆分为两个空列表。这被一遍又一遍地重复。为了阻止这种情况，每次使用追加函数时，都必须检查列表是否为空。
例如
I figured it out now after a bit of trolling the internet, so will answer it here if anyone else struggles with it.
The problem was that the append was creating an empty list. This list was passed as a parameter, then split again into two empty lists. And this was repeated over and over again. To stop this, everytime the append function is used, there must be a check if the lists are empty.
For example