12 Mar
2013
12 Mar
'13
5 a.m.
On Mar 12, 2013, at 12:44 AM, "Richard A. O'Keefe" <ok@cs.otago.ac.nz> 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 = <your_implementation_here> instance SumDP Period where date + period = <and_here>