Operator = {
    ADD         : function (leftVal, rightVal) { return leftVal + rightVal; },
    SUBTRACT    : function (leftVal, rightVal) { return leftVal - rightVal; },
    MULTIPLY    : function (leftVal, rightVal) { return leftVal * rightVal; },
    DIVIDE      : function (leftVal, rightVal) { return leftVal / rightVal; },
    
    EQUALS      : function (leftVal, rightVal) { return (leftVal == rightVal) ? 1 : 0; },
    NOTEQUALS   : function (leftVal, rightVal) { return (leftVal != rightVal) ? 1 : 0; },
    
    GT          : function (leftVal, rightVal) { return (leftVal > rightVal) ? 1 : 0; },
    LT          : function (leftVal, rightVal) { return (leftVal < rightVal) ? 1 : 0; },
    GTEQ        : function (leftVal, rightVal) { return (leftVal >= rightVal) ? 1 : 0; },
    LTEQ        : function (leftVal, rightVal) { return (leftVal <= rightVal) ? 1 : 0; },
    
    BOOLEAN_OR  : function (leftVal, rightVal) { ((leftVal != 0) || (rightVal != 0)) ? 1 : 0; },
    BOOLEAN_AND : function (leftVal, rightVal) { ((leftVal != 0) && (rightVal != 0)) ? 1 : 0; }
};

function VariablesHolder() {
    this.variables = {};
}
VariablesHolder.prototype.init = function () {
    this.variables = {
        "True": 1,
        "False": 0
    };
};
VariablesHolder.prototype.getVariable = function (name) {
    if (name in this.variables) {
        return this.variables[name];
    }
    return 0;
};
VariablesHolder.prototype.setVariable = function (name, value) {
    this.variables[name] = value;
};
Variables = new VariablesHolder();

function BinaryExpression(op, left, right) {
    this.op = op;
    this.left = left;
    this.right = right;
}
BinaryExpression.prototype.eval = function () {
    return this.op(this.left.eval(), this.right.eval());
};

function ValueExpression(value) {
    this.value = value;
}
ValueExpression.prototype.eval = function () {
    return this.value;
};

function VariableExpression(variable) {
    this.variable = variable;
}
VariableExpression.prototype.eval = function () {
    return Variables.getVariable(this.variable);
};