On Sun, Aug 31, 2008 at 4:21 PM, Jonathan Cast <[EMAIL PROTECTED]> wrote: > It seems as if you're proposing that > > doubleSet :: Set.Set Int -> Set.Set Int > doubleSet = map (*2) > > doubleList :: [Int] -> [Int] > doubleList :: map (*2) > > work, but that you not be allowed to notice that the definitions are > identical and substitute > > double = map (*2) > > for both definitions.
Yes, that's exactly what I am suggesting. This is especially important because Set cannot be made an instance of Functor because of the Ord restriction on the elements, so you can't generalize to fmap without redefining Functor as RestrictedFunctor or some such, which adds a ton of additional type-level programming that shouldn't be required for day-to-day work. I'm not against being able to use "double = map (*2)" generally, but the evidence I've seen says that the PL theory isn't there yet to do so without unacceptable performance penalties. (That definition violates the monomorphism restriction anyways). > Sorry, but I use Haskell specifically because I do *not* want to use C++. I don't think "a language I dislike also has this feature" is a good argument against a feature. C++ also has named fields in records, and a standard I/O library. Should Haskell not have those either? -- ryan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
