Hello all why the folowing is not allowed even with all extensions enabled both in Hugs and GHC? class BufStream h where class CharStream h where instance (CharStream h) => BufStream h where class MemoryStream h where instance (MemoryStream h) => BufStream h where i plan to implement many streams, some of which are supporting getBuf/putBuf interface of MemoryStream, and some getChar/putChar interface of CharStream and then automatically derive BufStream using the appropriate operations. but that just fail how can i pass around these restriction? can this be supported in future Hugs/GHC versions? ... just now i encountered this problem again: -- Copy entire contents of Stream to another Stream class (Stream h1, Stream h2) => StreamCopying h1 h2 where copyStream :: h1 -> h2 -> IO () instance (MemoryStream h1, BufStream h2) => StreamCopying h1 h2 where copyStream h1 h2 = return () instance (BufStream h1, MemoryStream h2) => StreamCopying h1 h2 where copyStream h1 h2 = return () -- Best regards, Bulat mailto:bulatz@HotPOP.com