public BasicSingleInputStream function(String extensionNamespace, String functionName,
                                           Expression... parameters) {

        streamHandlers.add(new StreamFunction(extensionNamespace, functionName, parameters));
        return this;
    }
Basic single input stream using filters, windows and functions
modules/siddhi-query-api/src/main/java/io/siddhi/query/api/execution/query/input/stream/BasicSingleInputStream.java