Hi, I'm looking for a way of comparing Ptrs to null *elegantly*. The FFI distinguishes between 'Ptr a' and 'FunPtr a', so testing would mean writing ((==) null[Fun]Ptr). This is rather tedious and a predicate 'isNull' might be in order so that it's possible to write when (isNull p) $ ... or throwIOErrorIf isNull ... , especially without having to worry about comparing against the correct null pointer (FunPtr or Ptr). That's something where a class can help, but I'm not sure whether such a specialised class is desired... I'd like to add the following class and instances/functions to Foreign.Ptr if nobody objects, they'd make code much more readable and concise: class ToPtr a where toPtr :: a -> Ptr b isNull :: ToPtr a => a -> Bool isNull = (==) nullPtr . toPtr The ToPtr class was suggested my Simon M. in favour of an even more specialised class PtrCmp which just has nullPtr :: PtrCmp a => isNull a -> Bool. -- Volker Stolz * http://www-i2.informatik.rwth-aachen.de/stolz/ * PGP * S/MIME