Running prolog in Android

Question

I am testing tuProlog in Android. I have an Activity TuProlog, class Parser to interact with prolog code and data.pl which contains prolog code. I can run it fine as a java project with output to console but I am facing trouble doing so as an Android project. For Android I get FileNotFoundException even though my file data.pl is copied in root of project, inside src and inside my package. I just want to fetch the result as string and display my result in TextView. Here are my codes

public class TuProlog extends Activity implements OnClickListener{

TextView tv;
Button b1;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    tv = (TextView)findViewById(R.id.label);
    b1 = (Button)findViewById(R.id.button1);
    b1.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    Parser custom = new Parser();
    String result = custom.parse();
    tv.setText(result);
}   
}


public class Parser {

Prolog engine;
PrintStream orgStream   = System.out;

ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream psout = new PrintStream(baos, Boolean.TRUE); // Using autoFlush
String myResult ;

public String parse()
{
    engine  = new Prolog();
    try{
        Theory t = new Theory(new FileInputStream("data.pl"));
        try{
            engine.setTheory(t);
            try{
                SolveInfo answer = engine.solve("likes(john,X).");
                try{
                    Term derivative = answer.getTerm("X");
                    return myResult;;
                }
                catch (NoSolutionException e){
                    e.printStackTrace();
                }
                catch (UnknownVarException e){
                    e.printStackTrace();
                }
            }
            catch (MalformedGoalException e){
                e.printStackTrace();
            }
        }
        catch (InvalidTheoryException e){
            e.printStackTrace();
        }
    } 
    catch (FileNotFoundException e){
        e.printStackTrace();
    }
    catch (IOException e){
        e.printStackTrace();
    }
    return null;
}
    @Override
public void onSpy(SpyEvent e) {
    // TODO Auto-generated method stub
    Log.d("TAG", "** LG'd onSpy => SpyEvent Occured ** " );
    System.out.println("** onSpy => SpyEvent Occured ** \n ");
    myResult =  e.getMsg();
}


@Override
public void onOutput(OutputEvent e) {
    // TODO Auto-generated method stub
     Log.d("TAG", "** LG'd: onOutput => OutputEvent Occured ** " );
        System.out.println("** onOutput => OutputEvent Occured ** \n ");
        myResult =  e.getMsg();

}


@Override
public void onWarning(WarningEvent e) {
    // TODO Auto-generated method stub
    Log.d("TAG", "** LG'd: onWarning => WarningEvent Occured ** " );
    System.out.println("** onWarning => WarningEvent Occured ** \n ");
    myResult = e.getMsg();
}
}

Data.pl

likes(john,mary).
likes(mary,wine).

Here is my logcat output, I dont know about System.err

04-15 18:51:25.480: W/System.err(23813): java.io.FileNotFoundException: /data.pl (No such file or directory)
04-15 18:51:25.484: W/System.err(23813): at org.apache.harmony.luni.platform.OSFileSystem.open(Native Method)
04-15 18:51:25.484: W/System.err(23813): at dalvik.system.BlockGuard$WrappedFileSystem.open(BlockGuard.java:232)
04-15 18:51:25.484: W/System.err(23813): at java.io.FileInputStream.<init>(FileInputStream.java:80)
04-15 18:51:25.484: W/System.err(23813): at java.io.FileInputStream.<init>(FileInputStream.java:132)
04-15 18:51:25.484: W/System.err(23813): at com.tuprolog.alicia.Parser.parse(Parser.java:32)
04-15 18:51:25.484: W/System.err(23813): at com.tuprolog.alicia.TuProlog.onClick(TuProlog.java:51)
04-15 18:51:25.484: W/System.err(23813): at android.view.View.performClick(View.java:2485)
04-15 18:51:25.484: W/System.err(23813): at android.view.View$PerformClick.run(View.java:9080)
04-15 18:51:25.484: W/System.err(23813): at android.os.Handler.handleCallback(Handler.java:587)

Answer 1

I get FileNotFoundException even though my file data.pl is copied in root of project

But look at the error:

java.io.FileNotFoundException: /data.pl (No such file or directory)

It's trying to read data.pl from root of the file system!

You could try using FileInputStream(File) constructor for more control over the path. Have a look at for example this question on how to get application's directory.

Answer 2

1. In eclipse, create a folder "plFiles" in the res folder of your project
2. Move your pl files to this folder (eg: res/plFiles/data.pl)

3. Use the activity to access this file using (a is the current activity)

   InputStream in = a.getResources().openRawResource(R.plFiles.data);
   

4. The above line returns an InputStream. You may now use Scanner or BufferedReader or any reader class of your liking to continue parsing or reading the file.

Another way to access files is mentioned here ... Access resource files in Android

Answer 3

I've done it before and have posted the (very, very beta proof of concept only) source code for interrogation, pls see below.

To download the Eclipse (Helios) project Source Code, goto: versaggi.biz, Downloads Adrea, TuProlog Dev Project, Eclipse (Helios) Java Source Project, and finally to TuProlog Android Eclipse Porject Source. That should get you started. Please keep in mind that this is proof of concept code ONLY and is will be completely rewritten before the final version is released. Given that, it does work well enough for you to get some insights into how I did what I did. If you want any assistance at all just contact me directly and I'll be glad to help you along. :-)