Proposal: Num instance for tuples

Brent Yorgey byorgey at
Thu Oct 18 16:44:13 CEST 2012

On Thu, Oct 18, 2012 at 11:58:17AM +0200, Twan van Laarhoven wrote:
> 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.

I am +1 for this proposal, but only as long as these instances are not
exported by the Prelude.  They are useful when you know you want them
but will confuse newbies -- based on evidence from #haskell, where
lambdabot has such instances in scope.


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