Hello Duncan, Monday, January 30, 2006, 9:02:48 PM, you wrote: DC> class IStream s where DC> readBlock :: s -> IO Block DC> data IStream = IStream { DC> istream_readBlock :: IO Block DC> } DC> instance IStream IStream where DC> readBlock s = istream_readBlock s DC> abstractIStream :: IStream s => s -> IStream DC> abstractIStream s = IStream { istream_readBlock = readBlock s } how that is done in my lib: class (Monad m) => Stream m h | h->m where vClose :: h -> m () vIsEOF :: h -> m Bool ..... data Handle = forall h . (Stream IO h) => Handle h instance Stream IO Handle where vClose (Handle h) = vClose h vIsEOF (Handle h) = vIsEOF h ..... -- Best regards, Bulat mailto:bulatz@HotPOP.com