Hello Robert, Tuesday, February 07, 2006, 6:42:41 PM, you wrote:
More disturbing is the complete inability to write general functions over tuples.
RD> As I understand it, you still have to write down the instance RD> declarations when using '-fgenerics'. only one generic instance. it's very much these ideas of using nested tuples, only with special syntax. below is my definitions of Binary class for types with only one constructor: class Binary a where -- | Convert value to sequence of bits and write it to the stream put_ :: (BinaryStream m h) => h -> a -> m () -- | Read value written to the stream as bit sequence get :: (BinaryStream m h) => h -> m a {- Using "generic type classes" extension, GHC allows to semi-automatically generate instances of Binary for any types. All what you need to define Binary instance for some type MyType is to write: instance Binary MyType where These is the all definitions required, but they don't work because of current restrictions in GHC's generics support: put_ {| Unit |} h Unit = return () put_ {| a:*:b |} h (x :*: y) = do put_ h x; put_ h y get {| Unit |} h = return () get {| a:*:b |} h = do x <- get h; y <- get h; return (x :*: y) -} -- Best regards, Bulat mailto:bulatz@HotPOP.com