ffi.hs

{-# LANGUAGE QuasiQuotes #-}
{-# LANGUAGE TemplateHaskell #-}

import Data.ByteString
import Data.ByteString.Unsafe
import Data.Time.Clock
import qualified Language.C.Inline as C
import qualified Language.C.Inline.Unsafe as CU

C.context (C.baseCtx <> C.bsCtx)

C.include "<stdlib.h>"

C.include "<string.h>"

measureTime :: IO a -> IO a
measureTime f = do
  t0 <- getCurrentTime
  a <- f
  t1 <- getCurrentTime
  print $ diffUTCTime t1 t0
  return a

alloc3BS :: IO ByteString
alloc3BS = do
  buf <-
    [C.block| char * {
      char *buf = malloc(3);
      return strncpy(buf, "ok!", 3);
     } |]
  -- buf :: _
  unsafePackMallocCStringLen (buf, 3)

main :: IO ()
main = do
  bs <- alloc3BS
  print bs