inline-c-example.hs

{-# LANGUAGE DisambiguateRecordFields #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}

module A where

import Data.ByteString
import Language.C.Inline as C

C.context $ baseCtx <> bsCtx
C.include "<string.h>"

newtype Char20 = Char20 ByteString

data MyStruct = MyStruct
  { id :: Char20
  , a  :: Int
  }

swing :: MyStruct -> IO ()
swing MyStruct{id = Char20 id_bs, a} =
  [C.block| void {
    typedef struct MyStruct {
      unsigned char id[20];
      int a;
    } MyStruct;
    void swing(MyStruct ms);

    MyStruct ms = {.a = $(int a_c)};
    strncpy((char*) ms.id, $bs-cstr:id_bs, sizeof ms.id);
    swing(ms);
  } |]
  where
    a_c = fromIntegral a