{-  
  
install my lib: https://github.com/KonstantinDjairo/haskell-obj-c

then:

  $ ghc -package-env - appleKit.hs -o hello \
  -package haskell-obj-c \
  -package libffi \
  -framework AppKit
  
  
-}


import Foreign.C.String (withCString)
import Foreign.LibFFI (argPtr, retPtr, retVoid, retCULong)
import Foreign.Ptr (castPtr)
import ObjC.Runtime

main :: IO ()
main = withAutoreleasePool $ do
  loadFramework "AppKit"

  appClass <- getRequiredClass "NSApplication"
  _ <- sendClassMsg appClass (mkSelector "sharedApplication")
         (retPtr retVoid) []

  alertClass <- getRequiredClass "NSAlert"
  alertPtr <- sendClassMsg alertClass (mkSelector "new")
                (retPtr retVoid) []
  let alert = RawId (castPtr alertPtr)

  stringClass <- getRequiredClass "NSString"
  title <- makeString stringClass "Hello from Haskell"
  detail <- makeString stringClass "RawId-only AppKit test."

  let RawId titlePtr = title
      RawId detailPtr = detail

  _ <- sendRawMsg alert (mkSelector "setMessageText:")
         retVoid [argPtr titlePtr]

  _ <- sendRawMsg alert (mkSelector "setInformativeText:")
         retVoid [argPtr detailPtr]

  _ <- sendRawMsg alert (mkSelector "runModal")
         retCULong []

  pure ()

makeString :: Class -> String -> IO RawId
makeString cls s =
  withCString s $ \cs -> do
    ptr <- sendClassMsg cls (mkSelector "stringWithUTF8String:")
             (retPtr retVoid) [argPtr cs]
    pure (RawId (castPtr ptr))