# Calling custom code By calling custom code, you can accomplish various use cases, including: * Integration of legacy systems lacking other interfaces * IoT integration for embedded devices/microcontrollers * Integration of software libraries to introduce new functionality {% hint style="info" %} This advanced feature requires programming knowledge. If uncertain about its applicability or how to use it, please [talk to us](mailto:support@heisenware.com), and we'll be happy to assist you. {% endhint %} ## VRPC VRPC (Variadic Remote Procedure Calls) is the open-source technology that enables calling custom code in Heisenware. Developed and maintained by the Heisenware team, VRPC seamlessly integrates into the Heisenware platform and apps developed with it. It allows direct calls between functions written in any programming language. Functions integrated with VRPC appear as custom functions in the App Builder's functions panel. To make custom functions available in the App Builder, you need to implement an adapter, sometimes referred to as code adapter, within the code to be integrated. The adapter wraps around existing functions non-intrusively and standardizes their interface. Refer to the [VRPC developer documentation](https://vrpc.io/docs) for details on implementing an adapter and calling custom code. Adapters are available for: * C++ * Node.js * R * React * Arduino Adapters for Python and other programming languages can be provided upon request. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.heisenware.com/~/changes/eYCCpn9cCBKOYnZA6a8f/building-apps/data-integration/calling-custom-code.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.