Question

我有一个事实数据库，其中包含这样的片段

symptom(shingles,headache).    
symptom(shingles,fever).    
symptom(shingles,malaise).    
symptom(shingles,headache).    
symptom(shingles,itching).    
symptom(shingles,hyperesthesia).    
symptom(shingles,paresthesia).   

test(shingles,blood).    
test(shingles,pcr).   

locale(shingles,all).  

treatment(shingles,calamine).    
treatment(shingles,aciclovir).

treatment(shingles,valaciclovir).    
treatment(shingles,famciclovir).    
treatment(shingles,corticosteroids).

然后我有一个谓词，可从用户那里获取症状列表。

getSymptoms(Symptoms) :-
    write('Please enter symptoms now, enter "Done" when finished: ' ),
    read_string(user, "\n", "\r", _, Response),
    (
        Response == "Done"
    ->
        Symptoms = []
    ;
        getSymptoms(Symptoms0),
        Symptoms = [Response|Symptoms0]
    ).

我的问题是如何将用户症状列表与第二个原子事实症状进行比较，然后将该疾病添加到另一个列表中？例如，用户输入发烧。由于发烧是带状疱疹的症状，因此会将带状疱疹添加到清单中。

Answer 1

这将起作用，但是允许输入重复的症状。我现在将其发布，以便您可以看到转换的第一部分，并且当我开始工作时将发布没有重复的部分。

getSymptoms(Symptoms) :-
    write('Please enter symptoms now, enter "Done" when finished: ' ),
    read_string(user, "\n", "\r", _, Response),
    (
        Response == "Done"
    ->
        Symptoms = []
    ;
        atom_string(Symptom,Response),
        valid_symptom(Symptom,Symptoms)
    ).

valid_symptom(Symptom,Symptoms) :-
    (
        symptom(_,Symptom)
    ->
        % Symptom was valid
        % so get next symptom and
        % add to list on backtracking
        getSymptoms(Symptoms0),
        Symptoms = [Symptom|Symptoms0]
    ;
        % Symptom was invalid
        % so warn user of invalid symptom and what they input
        % and get next symptom.
        % Do not add invalid Symptom to list on backtracking.
        format('Invalid symptom: `~w''~n',[Symptom]),
        getSymptoms(Symptoms0),
        Symptoms = Symptoms0
    ).

由于输入的值是字符串，而症状是symptom/2事实中的原子，因此需要将输入转换为原子进行比较。这是通过atom_string/2

完成的

atom_string(Symptom,Response)

如果症状无效，则向用户提供反馈format/2。最好使用write/1，因为它可以让您更好地控制输出。

format('Invalid symptom: `~w''~n',[Symptom])

如果输入的无效值是一种症状，则不应将其添加到列表中。这是经典的if / then类型的场景，并且在Prolog中使用->/2完成。这是标准模板

(
    <conditional>
->
    <true branch>
;
    <false branch>
)

条件是

symptom(_,Symptom)

还附带条件，通知它读取symptom/2事实，并忽略复合结构的第一部分，即_，并将输入的症状与事实中的症状进行匹配。比较是完成的，但这是通过统一完成的，而不是通过比较谓词（例如==/2）来完成的。

真实分支与以前相同

getSymptoms(Symptoms0),
Symptoms = [Symptom|Symptoms0]

但是假分支是

format('Invalid symptom: `~w''~n',[Symptom]),
getSymptoms(Symptoms0),
Symptoms = Symptoms0

请注意，无效的Symptom不会与[Symptom|Symptoms0]一起添加到列表中，并且两个分支（真和假）都应更新相同的变量Symptoms，在假变量中分支是通过Symptoms = Symptoms0完成的，valid_symptom/2不是分配，而是=/2（统一）。

getSymptoms/1的代码可能已与?- getSymptoms(Symptoms). Please enter symptoms now, enter "Done" when finished: wrong Invalid symptom: `wrong' Please enter symptoms now, enter "Done" when finished: headache Please enter symptoms now, enter "Done" when finished: malaise Please enter symptoms now, enter "Done" when finished: headache Please enter symptoms now, enter "Done" when finished: Done Symptoms = [headache, malaise, headache].内联，但是我将其拔出了，以便您查看如何完成以防将来需要这样做。

示例运行：

getSymptoms(Result) :-
    getSymptoms_helper([],Result).

getSymptoms_helper(Symptoms,Result) :-
    write('Please enter symptoms now, enter "Done" when finished: ' ),
    read_string(user, "\n", "\r", _, Response),
    (
        Response == "Done"
    ->
        Result = Symptoms
    ;
        atom_string(Symptom,Response),
        valid_symptom(Symptom,Symptoms,Result)
    ).

valid_symptom(Symptom,Symptoms,Result) :-
    (
        memberchk(Symptom,Symptoms)
    ->
        % Symptom was a duplicate
        % Do not add duplicate Symptom to list.
        getSymptoms_helper(Symptoms,Result)
    ;
        (
            symptom(_,Symptom)
        ->
            % Symptom was valid
            % so get next symptom and
            % add to list.
            getSymptoms_helper([Symptom|Symptoms],Result)
        ;
            % Symptom was invalid
            % so warn user of invalid symptom and what they input
            % and get next symptom.
            % Do not add invalid Symptom to list.
            format('Invalid symptom: `~w''~n',[Symptom]),
            getSymptoms_helper(Symptoms,Result)
        )
    ).

这是在构建列表时删除重复项的下一个变体。

Symptoms

此处的主要更改是累加器getSymptoms_helper穿过谓词，以便可以构建有效症状列表并将其用于测试下一个输入值。由于累加器需要在开始时进行初始化，因此将先前的谓词重命名为getSymptoms_helper([],Result)，以便可以使用

初始化累加器。

[]

通向

的通知

getSymptoms_helper(Symptoms,Result)

Symptoms

因此将[]的初始值设置为Done。

输入Result时，列表将与Symptoms0统一，并在反向链接时返回。通常，这些变量将分别命名为Symptoms和Symptom，但我将其保留为这种方式，以便于跟踪。否则，会有变量Symptoms，Symptoms0和?- getSymptoms(Symptoms). Please enter symptoms now, enter "Done" when finished: headache Please enter symptoms now, enter "Done" when finished: malaise Please enter symptoms now, enter "Done" when finished: headache Please enter symptoms now, enter "Done" when finished: Done Symptoms = [malaise, headache].，但是一旦习惯了它们，就更容易理解了。

使用memberchk/2进行重复检查比使用member/2进行检查要好。再次，这为混合添加了另一个条件。

示例运行：

import sys
exe = sys.executable

如何将列表与数据库Prolog比较

1 个答案: