Lib.hs

{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE TemplateHaskell          #-}

module Lib
  (islVersion)
  where

import Lib.Internal
import Foreign.C.Types
import Foreign.C.String

islVersion :: IO String
islVersion = peekCString =<< cisl_version

Lib_Internal.hs

{-# LANGUAGE TemplateHaskell #-}

module Lib.Internal where

import Foreign.C.String (CString)
import Lib.Internal.TH

-- Illegal type variable name: ‘CString’
--    When splicing a TH declaration:
--      foreign import ccall unsafe "isl_version" cisl_version :: GHC.Types.IO Foreign.C.String.CString

$(generateDecl "cisl_version")

Lib_Internal_TH.hs

{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE QuasiQuotes              #-}
{-# LANGUAGE TemplateHaskellQuotes    #-}
module Lib.Internal.TH where

import Language.Haskell.TH (Q, Dec(..), Callconv(..), Safety(..), Type(..), lookupTypeName, mkName)
import Language.Haskell.TH.Syntax (Foreign(..))

generateDecl :: String -> Q [Dec]
generateDecl fname = do
  let name = mkName fname
  Just io <- lookupTypeName "IO"
  Just cstring <- lookupTypeName "CString"
  let retType = AppT (VarT io) (VarT cstring)
  let dec = ForeignD $ ImportF CCall Unsafe "isl_version" name retType
  return [dec]