How to use the less/tree.Anonymous function in less

eval: function (env) {
        var args = this.args.map(function (a) { return a.eval(env) });

        if (this.name in tree.functions) { // 1.
            return tree.functions[this.name].apply(tree.functions, args);
        } else { // 2.
            return new(tree.Anonymous)(this.name +
                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")");
        }
    },

e: function (str) {
        return new(tree.Anonymous)(str);
    },
    '%': function (quoted /* arg, arg, ...*/) {

eval: function (env) {
        var args = this.args.map(function (a) { return a.eval(env) });

        if (this.name in tree.functions) { // 1.
            return tree.functions[this.name].apply(tree.functions, args);
        } else { // 2.
            return new(tree.Anonymous)(this.name +
                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")");
        }
    },

e: function (str) {
        return new(tree.Anonymous)(str);
    },
    '%': function (quoted /* arg, arg, ...*/) {

eval: function (env) {
        var args = this.args.map(function (a) { return a.eval(env) });

        if (this.name in tree.functions) { // 1.
            return tree.functions[this.name].apply(tree.functions, args);
        } else { // 2.
            return new(tree.Anonymous)(this.name +
                   "(" + args.map(function (a) { return a.toCSS() }).join(', ') + ")");
        }
    },

url: function () {
                    var value;

                    if (input.charAt(i) !== 'u' || !$(/url\(/g)) return;
                    value = $(this.entities.quoted) || $(/[-a-zA-Z0-9_%@$\/.&=:;#+?]+/g);
                    if (! $(')')) throw new(Error)("missing closing ) for url()");

                    return new(tree.URL)(value.value ? value : new(tree.Anonymous)(value));
                },

rule: function () {
                var value;
                var memo = i;

                if (name = $(this.property) || $(this.variable)) {
                    if ((name.charAt(0) != '@') && (match = peek(/([^@+\/*(;{}-]*);/g))) {
                        i += match[0].length - 1;
                        value = new(tree.Anonymous)(match[1]);
                    } else if (name === "font") {
                        value = $(this.font);
                    } else {
                        value = $(this.value);
                    }

                    if ($(this.end)) {
                        return new(tree.Rule)(name, value, memo);
                    } else {
                        furthest = i;
                        i = memo;
                    }
                }
            },

url: function () {
                    var value;

                    if (input.charAt(i) !== 'u' || !$(/url\(/g)) return;
                    value = $(this.entities.quoted) || $(/[-a-zA-Z0-9_%@$\/.&=:;#+?]+/g);
                    if (! $(')')) throw new(Error)("missing closing ) for url()");

                    return new(tree.URL)(value.value ? value : new(tree.Anonymous)(value));
                },

rule: function () {
                var value;
                var memo = i;

                if (name = $(this.property) || $(this.variable)) {
                    if ((name.charAt(0) != '@') && (match = peek(/([^@+\/*(;{}-]*);/g))) {
                        i += match[0].length - 1;
                        value = new(tree.Anonymous)(match[1]);
                    } else if (name === "font") {
                        value = $(this.font);
                    } else {
                        value = $(this.value);
                    }

                    if ($(this.end)) {
                        return new(tree.Rule)(name, value, memo);
                    } else {
                        furthest = i;
                        i = memo;
                    }
                }
            },

url: function () {
                    var value;

                    if (input.charAt(i) !== 'u' || !$(/url\(/g)) return;
                    value = $(this.entities.quoted) || $(/[-a-zA-Z0-9_%@$\/.&=:;#+?]+/g);
                    if (! $(')')) throw new(Error)("missing closing ) for url()");

                    return new(tree.URL)(value.value ? value : new(tree.Anonymous)(value));
                },