package linkage

Linkage - easier plugin loading for OCaml

Linkage provides an easy way for OCaml programs to dynamically load plugins. (Internally, Linkage uses OCaml's standard Dynlink module).

You specify the type your plugin provides by extending Linkage's plugin type. Here, we're defining a plugin which provides a single string -> int function:

type Linkage.plugin += MyPlugin of (int -> string)

The plugin is an ordinary OCaml module, which ends with a call to Linkage.provide:

let f = ...
...
Linkage.provide (MyPlugin f)

The main application then uses Linkage.load to load the plugin (here with only minimal error handling):

let f =
  match Linkage.load "plugins/plugin.cma" with
  | Ok (MyPlugin f) -> f
  | e -> Linkage.raise_error e

The plugin type (the Linkage.plugin += line) should be in a module by itself, since both the main application and the plugin depend on it. Only the main application and not the plugin should link against this module, to ensure that there's only one copy. If using OCamlbuild, you do this by omitting it from the plugin's .mllib file.

There are some working examples in the examples/ directory.