private ISet <string> GetVariables(Statement statement)
        {
            var variableCollector = new DependencyCollector();

            variableCollector.Collect(statement);
            return(variableCollector.Dependencies);
        }
        private ISet <string> GetVariables(Expression expression)
        {
            var variableCollector = new DependencyCollector();

            variableCollector.Collect(expression);
            return(variableCollector.Dependencies);
        }