Andreas Marth wrote:

As you might now already know I try to let VBA call Haskell via a DLL.

I had to do this a while ago; the best I could come up with was: 1. Make a Haskell DLL that exports plain C-style interface. 2. With Visual Studio, make a COM DLL that exports the interfaces to be used by VBA and passes the calls to the Haskell DLL. This COM DLL, among other things, handles the conversion between C-style strings and BSTR (there are examples on msdn.microsoft.com of doing this). Hope this helps. Cheers, Cyril