Re: Proposal: Num instance for (a -> b)

Monoid doesn't have fromInteger -like function. For example, we don't have FromString b => FromString (a -> b) instance. Unfortunately fromInteger is part of Num, so comparison with Monoid is unjust. Sent from my iPhone

On 11 Nov 2018, at 23.44, Daniel Cartwright wrote:

ANum seems to be just Data.Monoid.Ap. Also, I can see not wanting to worsen the error messages, though it is worth pointing out that we already have a Monoid instance with the same semantics, and a similar potential for confusing error messages.

...

On Sun, Nov 11, 2018, 1:36 AM Dan Burton

If this behavior is desired, you can use a newtype wrapper. As it happens, this fits the pattern of 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 wrote: On 11/11/18, Henning Thielemann 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... 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 _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

---

Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

---

Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries