jubnzv / ocaml-plugins-demo

A demo that shows how to use Findlib to implement a project with dynamically loaded plugins.

ocaml-plugins-demo

This project demonstrates how to use the Findlib library to implement a system with dynamically loaded plugins.

The project structured as follows:

• src/lib is a library that provides a public interface that must be implemented by plugins
• src/driver is an executable that loads and runs a given plugin
• src/plugin contains a demo plugin

The driver dynamically loads a compiled plugin that implements the Plugin module signature from the library. When running, the plugin transforms the provided input data.

The idea of this demo is to show that the same approach could be used to transform more complicated structures like ASTs using external plugins without recompiling the library or the driver.

Usage

Clone a repository and build the project from the source:

git clone https://github.com/jubnzv/ocaml-plugins-demo
cd ocaml-plugins-demo
dune build

To run the experiment, execute:

export OCAMLPATH=_build/install/default/lib
_build/default/src/driver/driver.exe demo_plugin test

The expected output is:

Registered: demo_plugin
Executing: demo_plugin
demo_plugin executed: test_demo

Under the hood the driver dynamically loads and executes the plugin demo_plugin.cxo on the input data "test". The plugin get the input string and transforms it adding the _demo suffix to it.

Alternative approaches

1. dune has its own plugins infrastructure. This requires inclusion of source code of plugins to the codebase.
2. janestreet/ocaml_plugin is a wrapper for Dynlink module that allows to compile OCaml source files and immediately link them using Dynlink. These modules must implement the interface present in the user's code.

References

1. OCaml library : Dynlink
2. OCaml - The dynlink library: dynamic loading and linking of object files
3. [Dune] Link against cmo / cmi without source? - Ecosystem - OCaml
4. dune: Findlib integration