Sorry, the parsing is tied to fromInteger. So i see what you mean about the
poor errors not being as comparable. Henning and another brought up a good
point, that either users ought to be warned or it would go in its own
module ala Text.Show.Function.
On Sun, Nov 11, 2018, 5:30 PM Daniel Cartwright I'm not quite sure the comparison is unjust - i was referring to +,-,*
giving strange error messages, not necessarily fromInteger. Recall that the
instance is Monoid b => Monoid (a -> b). An example is a user might mistakenly type `mempty "text"`, which is just
`const mempty`, though this might not be what they mean (GHC 8.6 will give
the hole in `f :: Text -> Text; f x = _ x;` a suggestion of `mempty`, which
might certainly be confusing to a beginner). Similarly `2 4` might parse 2
as being applied to 4, if (a -> b) had a Num instance (correct me if i'm
wrong in saying thats how such a string might be parsed). On Sun, Nov 11, 2018, 5:10 PM Oleg Grenrus 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 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 -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 On 11/11/18, Henning Thielemann 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
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