Re: [Haskell-cafe] Overloading

12.03.2013, 02:53, "Richard A. O'Keefe" :

On 12/03/2013, at 10:00 AM, MigMit wrote:

...

 On Mar 12, 2013, at 12:44 AM, "Richard A. O'Keefe" wrote:

...

 Prelude> :type (+)  (+) :: Num a => a -> a -> a

 The predefined (+) in Haskell requires its arguments and its result  to be precisely the same type.

 I think you had better justify the claim that Date+Period -> Date and  Date+Period -> Period are possible at the same time by showing us  actual code.  Ehm...

 import Prelude hiding (Num)  class SumDP a where (+) :: Date -> Period -> a  instance SumDP Date where date + period =  instance SumDP Period where date + period =

Notice the difference? I said that THE PREDEFINED (+) in Haskell requires its arguments and its result to be precisely the same type.

This example is not the predefined (+); it's another variable entirely that happens to have the same short name and cannot also add integers.

So? You've said:

I think you had better justify the claim that Date+Period -> Date and Date+Period -> Period are possible at the same time by showing us actual code.

You didn't say THIS (+) should be the "predefined" one. And, since you were replying to what Carlos said, and he didn't say it either, my code is still a valid example. Of course, you can refine your request so that it would mention the "predefined" (+), but that would be off-topic here.