Hello Ross, Friday, January 06, 2006, 2:16:24 PM, you wrote:
the following program fails to load in Hugs2005 with all Haskell extensions enabled:
instance (CharStream m h) => ByteStream m h where ... instance (ByteStream m h) => CharStream m h where ...
RP> Looks circular to me, i.e. there's no justification for inferring RP> instances of either class. However recent GHC's spot the recursion RP> in such cases and create mutually recursive instances. the following definition, which is a pure H98, also looks circular: class Something x where a::Int b::Int a = b+1 b = a-1 nevertheless, its semantics are well-known and obvious - instance need to define either a or b, and another function will be automatically derived. my instances definitions are just the same - you can define either functions in one class or in another, and then derive definitions for another class. i can't use single-class solution, because in actual code there are 4 different classes and in ideal someone can give explicit definition only for functions in one class and all other definitions must be derived automatically: class ByteStream s where getByte::Int class CharStream s where getChar::Char class BlockStream s where getBuf::Ptr a class MemoryStream s where receiveBuffer::Ptr a instance (ByteStream s) => CharStream s where getChar = chr getByte .... instance BlockStream Handle where .... instance CharStream StringBuffer where .... instance MemoryStream MemoryBuffer where .... -- Best regards, Bulat mailto:bulatz@HotPOP.com