Because I think that Prolog is very powerful  computer language  It was very  interesting for me to use it in my developments but as you see it is very hardly today use anything which is not   in  mainstream of computer technologies and as I wrote on the start page, my main development language at present is Java. Because Java has now very powerfull mechanism called "annotations" it opens for us very powerfull posibilities to make own metalanguages which will help us to develop software in other ways than it  dictates by imperative languages and Prolog I'm sure is one from the best languages to be used as a meta-language. Well, I developed own Java based prolog engine to use it as a meta-language and called it as PROL (cutted version of PROLog). The engine written to process prolog programms written in the Edinburgh Prolog style but not in the Turbo Prolog style. Of course you can say me that there are a lot of implementations of Prolog engine (and for Java too) already but I developed it to understand Prolog more precisily and to learn  its  basis (and to check my some ideas in the Prolog). It has been written in Java 1.6 and can't be used with early Java versions. Because the version is permanently reviewed, I don't publish the source codes but may be I'll make it in the future. May be the main useful thing which can be used in Java, it is the possibility to attach a Java object to a Prol Term and the object moves inside a Prol engine without change  as associated with the term-owner. You should understand and remember that it is just a small amateur project.

    As you see from the introduction, the engine based on the java annotation mechanism, it is used to define predicates and can be used to add prolog operators. The core of the prol engine work is the import com.igormaznitsa.prol.logic.ProlContext class which describes the context includes and a knowledge base. To make context you need an instance of a class which implements the com.igormaznitsa.prol.io.ProlStreamManager interface but as well you can use the default class DefaultProlStreamManagerImpl implements that interface. Then you can make consultation with an instance of  the com.igormaznitsa.prol.parser.ProlConsult class and the engine has been prepared for work. You can give goals to the engine with an instance of the com.igormaznitsa.prol.logic.Goal class and solve them with the solve() method of the class. If you want to make Java implementations of prolog predicates, you need to make own class extends  the abstract class com.igormaznitsa.prol.libraries.ProlAbstractLibrary and just to add it to a context which should use your library. I'd like to say that the JVM has not been written to work with very very deep stacks and I have very strange cases in the deep stack work (as well it is needed to use -Xss to increase the stack depth in Java), under Linux (Ubuntu) the JVM works with more deep stack than under Windows XP. The tail recursion is not implemented in the engine. The predicate list of the  prol core libraries (which are placed in the engine jar) can be read through the link.

   It is very easy to describe a predicate. As an example I show you how is implemented the SORT/2 predicate in the core library. As you can see you just need place @Predicate annotation before a function (which has a Goal and TermStruct as arguments).

If you want to define some operators in your library, you need use a ProlOperators annotation placed before the library class declaration and fill the annotation array with Operator annotations for every operator.

   Below you can see the source shows possibilities of the engine use in a Java program and show you the example which solves the Eight Queen task. The source below describes the task and will find all solutions for the Eight Queen chess task and print them.

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