/*
 * Load modules of code by enveloping them in a function and executing
 * the function: then they don't pollute the global namespace (unless they
 * assign to undeclared variables, but ES5 strict mode will prevent that.)
 * The wrapper function we create returns an evaluator function that 
 * evals a string inside the namespace. This evaluator function is the
 * return value of namespace() and provides read access to the symbols 
 * defined inside the namespace.
 */
function namespace(url) {
    if (!namespace.cache) namespace.cache = {};  // First call only
    if (!namespace.cache.hasOwnProperty(url)) {  // Only load urls once
        var code = gettext(url);           // Read code from url
        var f = new Function(code +        // Wrap code, add a return value
                             "return function(s) { return eval(s); };");
        namespace.cache[url] = f.call({}); // Invoke wrapper, cache evaluator
    }
    return namespace.cache[url];  // Return cached evaluator for this namespace
}


/* Return the text of the specified url, script element or file */
function gettext(url) {
    if (typeof XMLHttpRequest !== "undefined") { // Running in a browser
        if (url.charAt(0) == '#') {              // URL names a script tag
            var tag = document.getElementById(url.substring(1));
            if (!tag || tag.tagName != "SCRIPT")
                throw new Error("Unknown script " + url);
            if (tag.src) return gettext(tag.src);// If it has a src attribute
            else return tag.text;                // Otherwise use script content
        }
        else {                                   // Load file with Ajax
            var req = new XMLHttpRequest();
            req.open("GET", url, false);         // Asynchronous get
            req.send(null);
            return req.responseText;             // Error handling?
        }
    }
    else if (typeof readFile == "function") return readFile(url);  // Rhino
    else if (typeof snarf == "function") return snarf(url); // Spidermonkey
    else if (typeof read == "function") return read(url);   // V8
    else throw new Error("No mechanism to load module text");
}