Tau Prolog

A Prolog interpreter in JavaScript

Tau Prolog is a client-side Prolog interpreter fully implemented in JavaScript, whose development has been directed by the ISO Prolog Standard.

ISO Prolog Standard compliance. Tau Prolog development has been directed by the ISO Prolog Standard, designed to promote the applicability and portability of Prolog text and data among several data processing systems.

Compatible with browsers and Node.js. Tau Prolog has been developed to be used with either Node.js or a browser seamlessly. Just use the <script> tag or the require function to add Tau Prolog to your project and start coding.

DOM manipulation and event handling. Taking the best from JavaScript and Prolog, Tau Prolog allows you to handle browser events and modify the DOM of a web using Prolog predicates, making Prolog even more powerful.

Asynchronous predicates. Tau Prolog has been developed following a non-blocking, callback-based approach, allowing you, for instance, to sleep the main thread or to do AJAX requests without blocking the browser.

A brief look

1. Load the library

<script src="tau-prolog.js"></script>

2. Create a session

var session = pl.create();

3. Consult a program

session.consult(`
    likes(sam, salad).
    likes(dean, pie).
    likes(sam, apples).
    likes(dean, whiskey).
`, {
    success: function() { /* Program loaded correctly */ },
    error: function(err) { /* Error parsing program */ }
});

or

session.consult("path/to/src.pl", {
    success: function() { /* Program loaded correctly */ },
    error: function(err) { /* Error parsing program */ }
});

4. Query a goal

session.query("likes(sam, X).", {
    success: function(goal) { /* Goal loaded correctly */ },
    error: function(err) { /* Error parsing goal */ }
});

5. Look for answers

session.answer({
    success: function(answer) {
        console.log(session.format_answer(answer)); // X = salad ;
        session.answer({
            success: function(answer) {
                console.log(session.format_answer(answer)); // X = apples ;
            },
            // ...
        });
    },
    fail: function() { /* No more answers */ },
    error: function(err) { /* Uncaught exception */ },
    limit: function() { /* Limit exceeded */ }
});

This is a general scheme of how to use Tau Prolog:

// Consult
session.consult(program, {
    success: function() {
        // Query
        session.query(goal, {
            success: function(goal) {
                // Answers
                session.answer({
                    success: function(answer) { /* Answer */ },
                    error:   function(err) { /* Uncaught error */ },
                    fail:    function() { /* Fail */ },
                    limit:   function() { /* Limit exceeded */ }
                })
            },
            error: function(err) { /* Error parsing goal */ }
        });
    },
    error: function(err) { /* Error parsing program */ }
});

For further information, check the Documentation.

Downloads

You can download a custom bundle including only the modules you need here. Source code of Tau Prolog is available on GitHub. You can also install Tau Prolog from npm:

$ npm install tau-prolog

Documentation

Get Started with Tau Prolog

• A simple tutorial
• Compatibility with Node.js
• Manipulating the DOM with Prolog
• Making your own packages
• Promises interface
• Prototypes and Prolog objects

Prolog Predicate Reference

• Built-in predicates
• Lists module
• DOM module
• Random module
• Statistics module
• JavaScript module
• OS module
• CharsIO module
• Format module
• Concurrent module

License

Tau Prolog source code is released under the terms of the BSD 3-Clause License.