Hello Udo, Sunday, November 26, 2006, 5:21:29 PM, you wrote:
you shouldn't mix C++ template system with Haskell classes. C++ can't check templates at the time where template defined that leads to too late error messages. just imagine that improper definition of 'sum' will barks on each call site with a message that you can't use (&&) on Ints.
Instead it will tell you that there is no instance for (Boolean Int), and it will do so at every call site, assuming (&&) was indeed overloaded. Where's the difference? And conversely, a properly defined 'sum' will tell you that there is no instance for (Num String) at every wrong call site, which again is just the same, of course assuming that nobody made String into an instance of Num. Sounds like we're actually in violent agreement here.
seems that you never used type signatures. just try: sum :: Num a => [a] -> a sum = foldr1 (&&) -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com