Proposal: Num instance for (a -> b)

[Dan Burton]

-1, per the very confusing errors that would ensue.

If this behavior is desired, you can use a newtype wrapper. As it happens,
this fits the pattern of ANum <http://hackage.haskell.org/package/ANum>.
(Any Applicative can be made an instance of Num in this way.)

-- Dan Burton


On Sun, Nov 11, 2018 at 12:28 AM Tom Murphy <amindfv at gmail.com> wrote:

> On 11/11/18, Henning Thielemann <lemming at henning-thielemann.de> wrote:
> >
> > On Sun, 11 Nov 2018, Henning Thielemann wrote:
> >
> >> On Sat, 10 Nov 2018, Daniel Cartwright wrote:
> >>
> >>> relevant reddit comment
> >>> thread:
> https://www.reddit.com/r/haskell/comments/9vtis5/the_universe_of_discourse_i_hate_the_environment/e9f1lea?utm_so
> >>> urce=reddit-android
> >>
> >>
> https://wiki.haskell.org/index.php?title=Num_instance_for_functions&oldid=36632
> >>
> >> In short: It would make 2(x+y) no longer a type error but equivalent to
> 2.
> >> We
> >> would lose a lot of type safety for little syntactic gain.
> >
> > Btw. before adding more Wat instances please implement the GHC warning
> > about such instances:
> >     https://ghc.haskell.org/trac/ghc/ticket/11796
>
> This is my feeling as well.
>
> Tom
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