(function (tree) {

tree.Alpha = function (val) {
    this.value = val;
};
tree.Alpha.prototype = {
    type: "Alpha",
    accept: function (visitor) {
        this.value = visitor.visit(this.value);
    },
    eval: function (env) {
        if (this.value.eval) { this.value = this.value.eval(env) }
        return this;
    },
    toCSS: function () {
        return "alpha(opacity=" +
               (this.value.toCSS ? this.value.toCSS() : this.value) + ")";
    }
};

})(require('../tree'));