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

eval: function (args, env) {
        var frame = new(tree.Ruleset)(null, []), context;

        for (var i = 0, val; i < this.params.length; i++) {
            if (this.params[i].name) {
                if (val = (args && args[i]) || this.params[i].value) {
                    frame.rules.unshift(new(tree.Rule)(this.params[i].name, val.eval(env)));
                } else {
                    throw { message: "wrong number of arguments for " + this.name +
                            ' (' + args.length + ' for ' + this.arity + ')' };
                }
            }
        }
        return new(tree.Ruleset)(null, this.rules).evalRules({
            frames: [this, frame].concat(env.frames)
        });
    },
    match: function (args, env) {

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;
                    }
                }
            },

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;
                    }
                }
            },

tree.Rule.prototype.eval = function (context) {
    return new(tree.Rule)(this.name, this.value.eval(context));
};

eval: function (args, env) {
        var frame = new(tree.Ruleset)(null, []), context;

        for (var i = 0, val; i < this.params.length; i++) {
            if (this.params[i].name) {
                if (val = (args && args[i]) || this.params[i].value) {
                    frame.rules.unshift(new(tree.Rule)(this.params[i].name, val.eval(env)));
                } else {
                    throw { message: "wrong number of arguments for " + this.name +
                            ' (' + args.length + ' for ' + this.arity + ')' };
                }
            }
        }
        return new(tree.Ruleset)(null, this.rules).evalRules({
            frames: [this, frame].concat(env.frames)
        });
    },
    match: function (args, env) {

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;
                    }
                }
            },

tree.Rule.prototype.eval = function (context) {
    return new(tree.Rule)(this.name, this.value.eval(context));
};

eval: function (args, env) {
        var frame = new(tree.Ruleset)(null, []), context;

        for (var i = 0, val; i < this.params.length; i++) {
            if (this.params[i].name) {
                if (val = (args && args[i]) || this.params[i].value) {
                    frame.rules.unshift(new(tree.Rule)(this.params[i].name, val.eval(env)));
                } else {
                    throw { message: "wrong number of arguments for " + this.name +
                            ' (' + args.length + ' for ' + this.arity + ')' };
                }
            }
        }
        return new(tree.Ruleset)(null, this.rules).evalRules({
            frames: [this, frame].concat(env.frames)
        });
    },
    match: function (args, env) {

tree.Rule.prototype.eval = function (context) {
    return new(tree.Rule)(this.name, this.value.eval(context));
};