main.hs

{-# LANGUAGE MagicHash, UnboxedTuples #-}
module Main(main) where

import GHC.Exts         ( addrToAny# )
import GHC.Ptr          ( Ptr(..) )
import System.Info      ( os, arch )
import Encoding
import ObjLink

main :: IO ()
main = do initObjLinker
          loadObj "plugin.o"
          _ret <- resolveObjs
          ptr <- lookupSymbol (mangleSymbol Nothing "Plugin" "f")
          case ptr of
            Nothing -> putStrLn "Couldn’t load symbol"
            Just (Ptr addr) -> case addrToAny# addr of
                                 (# hval #) -> putStrLn hval

mangleSymbol :: Maybe String -> String -> String -> String
mangleSymbol pkg module' valsym =
  prefixUnderscore ++
  maybe "" (\p -> zEncodeString p ++ "_") pkg ++
  zEncodeString module' ++ "_" ++ zEncodeString valsym ++ "_closure"

prefixUnderscore :: String
prefixUnderscore =
  case (os,arch) of
    ("mingw32","x86_64") -> ""
    ("cygwin","x86_64") -> ""
    ("mingw32",_) -> "_"
    ("darwin",_) -> "_"
    ("cygwin",_) -> "_"
    _ -> ""

plugin.hs

module Plugin(f) where

f :: String
f = "Monads are just monoids in the category of endofunctors, what’s the problem?"

Main Post: https://purelyfunctional.org/posts/2016-05-20-dynamic-loading-haskell-module.html

Compile with ghc -package ghc -rdynamic main.hs