const annotation for Haskell FFI exports

I am exposing a Haskell function to C/C++ as

foreign export ccall foo :: Ptr CInt -> CInt -> IO CInt

foo ptr len = do
  list <- peekArray (fromIntegral len) ptr
  -- run calculation based on list entries
  return result

The signature of the exported function becomes

HsInt32 foo(HsPtr a1, HsInt32 a2);

However, since the array is not being modified, I would rather have this as

HsInt32 foo(const HsPtr a1, HsInt32 a2);

Is there a way to automatically add this annotation?

(The motivation is that I want this to operate on an std::vector< int > via

inline int foo(const std::vector<int> &v)
{
  return foo(v.data(), v.size());
}

without including a const_cast.)

const annotation for Haskell FFI exports

1 Answers