Maybe we could add default implementations using generics? Then such an instance would be one "deriving instance" line away.
Sjoerd
On Oct 18, 2012, at 11:58 AM, Twan van Laarhoven
Dear list,
One piece of utility code that I find myself writing over and over again is the pointwise Num instance for tuples, i.e.
instance (Num a, Num b) => Num (a,b) where fromInteger x = (fromInteger x, fromInteger x) (a,b) + (a',b') = (a + a', b + b') (a,b) - (a',b') = (a - a', b - b') (a,b) * (a',b') = (a * a', b * b') negate (a,b) = (negate a, negate b) abs (a,b) = (abs a, abs b) signum (a,b) = (signum a, signum b)
I therefore propose that this instance be added to the base library. If we do that, the equivalent instances for (,,) (,,,) etc. should perhaps also be added, as well as instances for other numeric classes such as Fractional and Floating.
Discussion period: 2 weeks, ends 2012-11-01.
Twan
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