ProscriptLS

Prolog for the Web

The ProscriptLS language is a version of Prolog that runs in web browsers. It supports interaction with the HTML Document Object Model (DOM) through builtin predicates. There is a full source-level Prolog debugger based on the Byrd Box Model available through an in-client command-line ProscriptLS interpreter.
The implementation uses a runtime engine that interprets byte codes. This engine is implemented in Javascript and is a version of the Warren Abstract Machine (WAM).

Running ProscriptLS

ProscriptLS is started by the proscript_init function (implemented in the proscriptls.js library). This function is typically invoked once per load of the web page in an onload handler for the 'body' element:

<body onload=
        "proscript_init();">
Body stuff
</body>

Compiling ProscriptLS programs in the web client

The proscript_init function supports compilation of ProscriptLS programs in the client using the 'script' tag with the 'type' attribute of 'text/prolog' or using the ProscriptLS 'consult/1' predicate.

Compilation Examples

  • The 'script' tag with the source being a file specified using the 'src' attribute:
    
    <script type="text/prolog"
            src="my_program.pl">
    </script>
    
  • The 'script' tag with the source as the text content of the 'script' element:
    
    <script type="text/prolog">
    my_program :-
        some_code.
    </script>
    
  • Consulting a source file using the proscript function:
    
    <body onLoad= "proscript( 'consult([my_program])');">
    More HTML
    </body>
    

Basic Example

The following HTML source is a basic example showing the use of a ProscriptLS program to create a 'click me' button that when clicked displays a 'Hello World' alert dialog.

<html lang="en">
<head>
    <title>ProscriptLS Basic</title>
</head>
<body onload="proscript_init();">
<div>
    <h2>ProscriptLS Basic</h2>
    <p>
        The button displays an alert
        dialog containing
        'Hello World'
    </p>
    <div id="basic"></div>
</div>
<script type="text/javascript"
        src="../proscriptls.js">
</script>
<script type="text/prolog">
:- initialization(setup_button).

setup_button :-
    dom_element_attribute_value(E, id, basic),
    create_dom_element('BUTTON', Button),
    create_dom_text_node("Click Me", NewContent),
    append_dom_node_child(Button, NewContent),
    dom_object_method(Button,
        addEventListener(click,
            alert('Hello World!'))),
    append_dom_node_child(E, Button).
</script>
</body>
</html>
The ':- initialization(setup_button).' statement in the Prolog source is a Prolog compiler directive that causes the wam_compiler to evaluate 'setup_button' after completing the compilation of the Prolog source in that 'script' element.