(I agree with the two Simons; just want to throw in a few more considerations.)
Just curious ... What's the use case, Frank? (It is probably related to debugging or assertion checking; do you have code details that you want to share?) Do you *really* want to do type-case on those multi-arity parametric types in the sense that you would care about keeping n, n-1, n-2, ..., 1 type positions polymorphic when casting? If you don't, then monomorphic instances of Typeable would be fine. And they are much easier to generate, indeed. (Typeable.h in the Data/include dir (ghc cvs) could be of help to solve the problem before GHC catches up.) It's perhaps useful to recall that the arity-sensitive Typeable business was introduced for the purpose of polymorphic type-case in the context of generic programming with SYB1 and 2 (a bit less at level 3) BTW, for the ICFP 2005 style of SYB (level 3), Typeable instances may be entirely avoidable, depending on programming style and scenario. All the best, Ralf (Once again, sounds like kind-polymorphism would simplify the implementation and the use of Haskell.) > -----Original Message----- > From: Simon Peyton-Jones > Sent: Wednesday, August 10, 2005 3:32 AM > To: Simon Marlow; 'Frank Huch'; 'glasgow-haskell-bugs@haskell.org' > Cc: Ralf Lammel > Subject: RE: Deriving Typeable instances > > Yes, you could I suppose. But then there'd be a different peculiar change > in behaviour at arity 7. I'm not sure that'd be an advantage. > > Simon > > | -----Original Message----- > | From: Simon Marlow > | Sent: 10 August 2005 10:58 > | To: Simon Peyton-Jones; Frank Huch; glasgow-haskell-bugs@haskell.org > | Subject: RE: Deriving Typeable instances > | > | On 09 August 2005 17:16, Simon Peyton-Jones wrote: > | > | > I'm not against this, although you can work around the problem by > | > adding a library that defines the missing type classes (Typeable8, > | > Typeable9 etc), and making your compiler generate the instance > | > itself. There is nothing magic about 'deriving'; it's just > | > convenient. > | > | If the arity is >7, couldn't we just generate a Typeable instance, > rather than the TypeableN instance? > | It would mean you wouldn't get the benefits of TypeableN, but at least > you'd have Typeable. > | > | Cheers, > | Simon _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
