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Using the Haskell Host SDK

Check your installation

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

1. Install the Haskell library​

Install via cabal from git:

Add the git repository to your cabal project:

source-repository-package
  type: git
  location: https://github.com/extism/extism.git
  subdir: haskell

Add the dependency to your cabal file:

library
  build-depends: extism

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.hs
module Main where

import Extism
import Extism.Manifest(manifest, wasmFile)

unwrap (Right x) = x
unwrap (Left (ErrorMessage msg)) = do
  error msg

main = do
  context <- Extism.newContext
  plugin <- unwrap <$> Extism.pluginFromManifest context (manifest [wasmFile "../wasm/code.wasm"]) False 
  res <- unwrap <$> Extism.call plugin "count_vowels" (Extism.toByteString "this is a test")
  putStrLn (Extism.fromByteString res)
  Extism.free plugin

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!