DavidA wrote:
I suspect that the answer to the question is, yes, you can have different Functor instances. All you need is a sum-product type that it's possible to interpret as two different abstractions, leading to two different Functor instances.
The sum-product types are exactly the "not-too-exotic" types to which my proof applies. So as long as extensional equivalence means Haskell equivalence, and not some "modulo an interpretation" equivalence (like considering two lists equivalent if they contain the same elements but in potentially different order), the answer is no, one cannot have different funtor instances. Ciao, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:[EMAIL PROTECTED] _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
