less.js/lib/less/tree/condition.js

module.exports = function (tree) {

var Condition = function (op, l, r, i, negate) {
    this.op = op.trim();
    this.lvalue = l;
    this.rvalue = r;
    this.index = i;
    this.negate = negate;
};
Condition.prototype = {
    type: "Condition",
    accept: function (visitor) {
        this.lvalue = visitor.visit(this.lvalue);
        this.rvalue = visitor.visit(this.rvalue);
    },
    eval: function (env) {
        var a = this.lvalue.eval(env),
            b = this.rvalue.eval(env);

        var i = this.index, result;

        result = (function (op) {
            switch (op) {
                case 'and':
                    return a && b;
                case 'or':
                    return a || b;
                default:
                    if (a.compare) {
                        result = a.compare(b);
                    } else if (b.compare) {
                        result = b.compare(a);
                    } else {
                        throw { type: "Type",
                                message: "Unable to perform comparison",
                                index: i };
                    }
                    switch (result) {
                        case -1: return op === '<' || op === '=<' || op === '<=';
                        case  0: return op === '=' || op === '>=' || op === '=<' || op === '<=';
                        case  1: return op === '>' || op === '>=';
                    }
            }
        })(this.op);
        return this.negate ? !result : result;
    }
};
return Condition;
};