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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​

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
  -- NOTE: if you encounter an error such as: 
  -- "Unable to load plugin: unknown import: wasi_snapshot_preview1::fd_write has not been defined"
  -- change `False` to `True` in the following function to provide WASI imports to your plugin.
  plugin <- unwrap <$> Extism.createPluginFromManifest (manifest [wasmFile "../wasm/code.wasm"]) False 
  res <- unwrap <$> 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!