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Using the OCaml Host SDK

Check your installation

Please be sure you've installed Extism before continuing with this guide.

1. Install the OCaml library​

Extism is not yet released on opam

Install via git:

opam pin extism https://github.com/extism/extism.git#main

2. Import the library and use the APIs​

Count Vowels Plugin

code.wasm in this example is our example plugin that counts vowels. If you want to run this, download it first and set the path:

curl https://raw.githubusercontent.com/extism/extism/main/wasm/code.wasm > code.wasm
main.ml
open Extism

let () =
  let input =
    if Array.length Sys.argv > 1 then Sys.argv.(1) else "this is a test"
  in
  let ctx = Context.create () in
  let manifest = Manifest.v [ Manifest.file "../wasm/code.wasm" ] in
  let plugin = Extism.of_manifest ctx manifest |> Result.get_ok in
  let res = Extism.call plugin ~name:"count_vowels" input |> Result.get_ok in
  print_endline res;
  Context.free ctx

Need help?​

If you've encountered a bug or think something is missing, please open an issue on the Extism GitHub repository.

There is an active community on Discord where the project maintainers and users can help you. Come hang out!