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

} else {
            context = [], env = { frames: [] }
            for (var i = 0; i < this.rules.length; i++) {
                if (this.rules[i] instanceof tree.Import) {
                    Array.prototype.splice
                         .apply(this.rules, [i, 1].concat(this.rules[i].eval(env)));
                }
            }
        }

        // push the current ruleset to the frames stack
        env.frames.unshift(this);

        // Evaluate mixins
        for (var i = 0; i < this.rules.length; i++) {
            if (this.rules[i] instanceof tree.mixin.Call) {
                Array.prototype.splice
                     .apply(this.rules, [i, 1].concat(this.rules[i].eval(env)));
            }
        }

        // Evaluate rules and rulesets
        for (var i = 0; i < this.rules.length; i++) {
            rule = this.rules[i];

            if (rule instanceof tree.Directive) {
                rulesets.push(rule.eval(env).toCSS(paths, env));
            } else if (rule.rules) {
                rulesets.push(rule.toCSS(paths, env));
            } else if (rule instanceof tree.Comment) {
                if (this.root) {
                    rulesets.push(rule.toCSS());

call: function () {
                    var elements = [], e, c, args, index = i;

                    while (e = $(/[#.][a-zA-Z0-9_-]+/g)) {
                        elements.push(new(tree.Element)(c, e));
                        c = $('>');
                    }
                    $('(') && (args = $(this.entities.arguments)) && $(')');

                    if (elements.length > 0 && ($(';') || peek('}'))) {
                        return new(tree.mixin.Call)(elements, args, index);
                    }
                },

}
            }
            return this.root.rules;
        }
    }
};
if (typeof(require) !== 'undefined' && typeof(__LESS_DIST__) === 'undefined') { var tree = require('less/tree') }

tree.Keyword = function Keyword(value) { this.value = value };
tree.Keyword.prototype = {
    eval: function () { return this },
    toCSS: function () { return this.value }
};
if (typeof(require) !== 'undefined' && typeof(__LESS_DIST__) === 'undefined') { var tree = require('less/tree') }

tree.mixin = {};
tree.mixin.Call = function MixinCall(elements, args, index) {
    this.selector = new(tree.Selector)(elements);
    this.arguments = args;
    this.index = index;
};
tree.mixin.Call.prototype = {
    eval: function (env) {
        var mixins, rules = [], match = false;

        for (var i = 0; i < env.frames.length; i++) {
            if ((mixins = env.frames[i].find(this.selector)).length > 0) {
                for (var m = 0; m < mixins.length; m++) {
                    if (mixins[m].match(this.arguments, env)) {
                        try {
                            Array.prototype.push.apply(
                                  rules, mixins[m].eval(this.arguments, env).rules);

}
};

tree.mixin.Definition = function MixinDefinition(name, params, rules) {
    this.name = name;
    this.selectors = [new(tree.Selector)([new(tree.Element)(null, name)])];
    this.params = params;
    this.arity = params.length;
    this.rules = rules;
    this._lookups = {};
    this.required = params.reduce(function (count, p) {
        if (p.name && !p.value) { return count + 1 }
        else                    { return count }
    }, 0);
};
tree.mixin.Definition.prototype = {
    toCSS: function () { return "" },
    variable: function (name) { return tree.Ruleset.prototype.variable.call(this, name) },
    find: function () { return tree.Ruleset.prototype.find.apply(this, arguments) },
    rulesets: function () { return tree.Ruleset.prototype.rulesets.apply(this) },

    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 this.root.rules;
        }
    }
};
if (typeof(require) !== 'undefined' && typeof(__LESS_DIST__) === 'undefined') { var tree = require('less/tree') }

tree.Keyword = function Keyword(value) { this.value = value };
tree.Keyword.prototype = {
    eval: function () { return this },
    toCSS: function () { return this.value }
};
if (typeof(require) !== 'undefined' && typeof(__LESS_DIST__) === 'undefined') { var tree = require('less/tree') }

tree.mixin = {};
tree.mixin.Call = function MixinCall(elements, args, index) {
    this.selector = new(tree.Selector)(elements);
    this.arguments = args;
    this.index = index;
};
tree.mixin.Call.prototype = {
    eval: function (env) {
        var mixins, rules = [], match = false;

        for (var i = 0; i < env.frames.length; i++) {
            if ((mixins = env.frames[i].find(this.selector)).length > 0) {
                for (var m = 0; m < mixins.length; m++) {
                    if (mixins[m].match(this.arguments, env)) {
                        try {
                            Array.prototype.push.apply(
                                  rules, mixins[m].eval(this.arguments, env).rules);
                            match = true;

}
};

tree.mixin.Definition = function MixinDefinition(name, params, rules) {
    this.name = name;
    this.selectors = [new(tree.Selector)([new(tree.Element)(null, name)])];
    this.params = params;
    this.arity = params.length;
    this.rules = rules;
    this._lookups = {};
    this.required = params.reduce(function (count, p) {
        if (p.name && !p.value) { return count + 1 }
        else                    { return count }
    }, 0);
};
tree.mixin.Definition.prototype = {
    toCSS: function () { return "" },
    variable: function (name) { return tree.Ruleset.prototype.variable.call(this, name) },
    find: function () { return tree.Ruleset.prototype.find.apply(this, arguments) },
    rulesets: function () { return tree.Ruleset.prototype.rulesets.apply(this) },

    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 + ')' };
                }

call: function () {
                    var elements = [], e, c, args, index = i;

                    while (e = $(/[#.][a-zA-Z0-9_-]+/g)) {
                        elements.push(new(tree.Element)(c, e));
                        c = $('>');
                    }
                    $('(') && (args = $(this.entities.arguments)) && $(')');

                    if (elements.length > 0 && ($(';') || peek('}'))) {
                        return new(tree.mixin.Call)(elements, args, index);
                    }
                },

}
            return this.root.rules;
        }
    }
};
if (typeof(require) !== 'undefined') { var tree = require('less/tree') }

tree.Keyword = function Keyword(value) { this.value = value };
tree.Keyword.prototype = {
    eval: function () { return this },
    toCSS: function () { return this.value }
};
if (typeof(require) !== 'undefined') { var tree = require('less/tree') }

tree.mixin = {};
tree.mixin.Call = function MixinCall(elements, args, index) {
    this.selector = new(tree.Selector)(elements);
    this.arguments = args;
    this.index = index;
};
tree.mixin.Call.prototype = {
    eval: function (env) {
        var mixins, rules = [], match = false;

        for (var i = 0; i < env.frames.length; i++) {
            if ((mixins = env.frames[i].find(this.selector)).length > 0) {
                for (var m = 0; m < mixins.length; m++) {
                    if (mixins[m].match(this.arguments, env)) {
                        try {
                            Array.prototype.push.apply(
                                  rules, mixins[m].eval(this.arguments, env).rules);
                            match = true;

}
            }
            return this.root.rules;
        }
    }
};
if (typeof(require) !== 'undefined') { var tree = require('less/tree') }

tree.Keyword = function Keyword(value) { this.value = value };
tree.Keyword.prototype = {
    eval: function () { return this },
    toCSS: function () { return this.value }
};
if (typeof(require) !== 'undefined') { var tree = require('less/tree') }

tree.mixin = {};
tree.mixin.Call = function MixinCall(elements, args, index) {
    this.selector = new(tree.Selector)(elements);
    this.arguments = args;
    this.index = index;
};
tree.mixin.Call.prototype = {
    eval: function (env) {
        var mixins, rules = [], match = false;

        for (var i = 0; i < env.frames.length; i++) {
            if ((mixins = env.frames[i].find(this.selector)).length > 0) {
                for (var m = 0; m < mixins.length; m++) {
                    if (mixins[m].match(this.arguments, env)) {
                        try {
                            Array.prototype.push.apply(
                                  rules, mixins[m].eval(this.arguments, env).rules);

this.rules.forEach(function (rule) {
            if (rule.evalRules) {
                rules.push(rule.evalRules(context));
            } else if (rule instanceof tree.mixin.Call) {
                Array.prototype.push.apply(rules, rule.eval(context));
            } else {
                rules.push(rule.eval(context));
            }
        });
        this.rules = rules;