06-JavaProlog

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Outline On Java-Prolog Integration Prolog calling Java Java calling Prolog Prolog libraries written in Java Projects in Prolog

06

Java-Prolog Integration

Mirko [email protected]

Ingegneria Due

Alma Mater StudiorumUniversita di Bologna a Cesena

Academic Year 2006/2007
http://find/http://goback/


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On Java-Prolog Integration

Prolog calling Java

Java calling Prolog

Prolog libraries written in Java

Projects in Prolog


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Advantages of Prolog

Declarative style of programming

Concise way of expressing algorithms and data structures

Intrinsic search & re-try mechanisms

Navigation abilities

Rapid prototyping

(More near to model abstract concepts)


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Advantages of Java

Imperative style of programming

More easy for the typical programmer More efficient than Prolog

Wide availability of libraries Graphics, Network, File-System, XML, . . .


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Why Java-Prolog integration

Mainstream Scenario

Using Java for everything

Using Prolog for nothing

The Proposed Scenario

Using Java for standard management and low-level aspects

Using Prolog for data & behaviour of the system model

Examples

In a MVC application, the model written in Prolog

In writing an agent, modelling its mind in Prolog

Sometimes, even accessing Java from Prolog to exploit theJVM

O l O J P l I P l ll J J ll P l P l l b J P P l


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public class C{

public static void main(String[] s){

javax.swing.JFrame f=new javax.swing.JFrame();

f.setSize(100,100);

f.setVisible(true);}

}

This is a simple case of a Java class that creates a window on

the screen using javax.swing library

O li O J P l I i P l lli J J lli P l P l lib i i i J P j i P l


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createframe(Name,X,Y):-

java_object(javax.swing.JFrame,[],Obj),

Obj


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Predicate java object/3

Signature

java object(+ClassName,+ArgumentList,-ObjRef)

ClassName is the package-qualified name Retrieved through the classpath of the 2P application

ArgumentList is a list of arguments for the constructor integers, strings, Java objects (see below)

ObjRef is a Prolog term used as Object reference it is of the kind $obj 2

It calls the Java construct of ClassName class, passingarguments, and the result is associated to handler ObjRef

Example

?- java_object(Integer,1,X).

Outline On Java Prolog Integration Prolog calling Java Java calling Prolog Prolog libraries written in Java Projects in Prolog


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Predicate


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Predicate returns/2

Signature

ObjRef


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Other predicates

Example

To read/write the field of an object

To create/access Java arrays

To load a class dynamically

. . .

Where learning more?

See document developer-guide.pdf in tuPrologdocumentation



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An example application: handling vectors

Want to handle vectors of integers in PrologProviding the following predicates

vector new(-VectorRef)

vector add(+VectorRef,+Element)

vector addall(+VectorRef,+OtherVectorRef)

vector clear(+VectorRef)

vector contains(+VectorRef,+Element)

vector lookup(+VectorRef,+Position,-Element)

vector isempty(+VectorRef,+Position,-Element)

vector size(+VectorRef,-Size)

vector print(+VectorRef)



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g g g g g g g j g

Some examples

Code

vector_new(V):-java_object(java.util.Vector,[],V).

vector_add(V,E):-java_object(java.lang.Integer,[E],I),

V


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The tuprolog Java library

The approach..Via an API providing:

Classes representing an engine, a term, a solution

Methods to solve goals, ask for other solutions, navigate terms

alice.tuprolog

Main Classes

Prolog: a Prolog Virtual Machine

Theory: a Prolog DB, as a text or list of clauses

SolveInfo: the outcome of a goal

Term: the interface to any term



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Direct Goal Solution

Working with the Prolog command-lineimport alice.tuprolog.*;

public class Test1 {

public static void main(String[] args) throws Exception {

Prolog engine = new Prolog();// Note: append is a built-in predicate!

SolveInfo info = engine.solve("append([1],[2,3],X).");

System.out.println(info.getSolution());

}

}Result

append([1],[2,3],[1,2,3])



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Getting all solutions


public static void main(String[] args) throws Exception {Prolog engine = new Prolog();

SolveInfo info = engine.solve("append(X,Y,[1,2,3]).");

while (info.isSuccess()){

System.out.println(

"solution: "+info.getSolution()+

" - bindings: X/"+info.getTerm("X")+" Y/"+info.getTerm("Y"));

if (engine.hasOpenAlternatives()){

info=engine.solveNext();

} else {

break;

} } } }

solution: append([],[1,2,3],[1,2,3]) - bindings: X/[] Y/[1,2,3]

solution: append([1],[2,3],[1,2,3]) - bindings: X/[1] Y/[2,3]

solution: append([1,2],[3],[1,2,3]) - bindings: X/[1,2] Y/[3]

solution: append([1,2,3],[],[1,2,3]) - bindings: X/[1,2,3] Y/[]



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The structure of Terms

Term, The root of the hierarchy

Methods:

getRenamedCopy: Changes the name of variables

isAtom: Is this a constant name or number?

isList: Is this a list?

unify: Does this unify with that?

Hierarchy

Term: The root of the hierarchy Var: A variable (with a name of anonymous) Number: int, float, and so on

Double, Float, Int, Long

Struct: a compound term, but also a list



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Creating and Using Terms



Prolog engine = new Prolog();

// [1]

Term list1=engine.toTerm("[1]");// [2,3]

Term list2=new Struct(new Term[]{new Int(2),new Int(3)});

// append([1],[2,3],X).

Term app=new Struct("append",list1,list2,new Var("X"));

SolveInfo info = engine.solve(app);

System.out.println(info.getSolution());} }



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Reading Terms




Term t=new Struct();

// t will be [0,1,2,...,9,10]

for (int i=10;i>=0;i--){t=new Struct(new Int(i),t);

}

Term app=new Struct("append",t,t,new Var("X"));

SolveInfo info = engine.solve(app);

Struct t2=(Struct)info.getTerm("X");

for(java.util.Iterator i=t2.listIterator();i.hasNext();){System.out.println(""+i.next());

} } }



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Setting a Theory




Theory t=new Theory(

"search(E,[E|_])."+"\n"+

"search(E,[_|L]):-search(E,L)."+"\n"

);

// engine.setTheory(new FileInputStream("file.pl"));

engine.setTheory(t);

SolveInfo info = engine.solve("search(1,[1,2,3]).");

System.out.println(""+info.getSolution());}

}



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Which applications?

Each time you want in Java something that is betterimplemented in Prolog

Example

Realise permutations over Lists

Permutation are easy implemented in Prolog by a predicateperm(+L,-L2)

Build a Java method that takes a LinkedList and returns aIterator, each time invokingsolveNext() and building the LinkedList from the result.



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Prolog Libraries

What is a Prolog Library?

It is basically a Prolog DB

It includes the definition of many predicates

It can be loaded in different ways:

From another theory through goal load library/1 In the 2P IDE through the library manager

Built-in examples

BasicLibrary: Standard operators, e.g. append. ISOLibrary: Standard operators of ISO standard

IOLibrary: for Input/Output, e.g. tell, told

They are all automatically added by 2P IDE



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Building a Library in Java

It is a very elegant approach

Write a Java class where each method defines a differentpredicate

Compile this class, e.g. with name lib.mylibrary

Load the library with load library(lib.mylibrary)

Structure of methods

public boolean (T1 arg1,...,Tn argN)

public Term (T1 arg1,...,Tn argN)

where Ti is either Term, Var, etc.



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A Simple Library

public class TestLibrary extends Library {// builtin functor sum(A,B)

public Term sum_2(Number arg0, Number arg1){

float arg0 = arg0.floatValue();

float arg1 = arg1.floatValue();

return new Float(arg0+arg1);}

// builtin predicate println(Message)

public boolean println_1(Struct arg){

System.out.println(arg);

return true;

}

}

test :- N is sum(5,6), println(N).



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Projects in Prolog

Building Prolog Libraries in Java

Accessing a DBMS via JDBC

Parsing an XML document, and transforming it using XSLT

. . .

Building Java Applications using Prolog

A game like chess, where the computer is played by Prolog

An application where a core is implemented in Prolog

. . .

Others related to Parsers and Languages

. . .



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06

Java-Prolog Integration

Mirko [email protected]

Ingegneria Due

Alma Mater StudiorumUniversita di Bologna a Cesena

Academic Year 2006/2007

Documents

06-JavaProlog