Fwiw, a less contrived, and much more relatable, version of Richard's
example would be
pattern Is3 :: (Num a, Eq a) => a -- only a Required constraint
pattern Is3 = 3 -- a polymorphic literal!
I think it can be quite instructive for people new to patsyn typing to work
out why this is exactly
> I'm afraid none of this is apparent from the User Guide -- and I even
> contributed some material to the Guide, without ever understanding that.
> Before this thread, I took it that 'Required' means for building -- as in for
> smart constructors.
No, that's not what the required/provided
If you haven't yet, it is probably a good idea to read section 6 of
https://gergo.erdi.hu/papers/patsyns/2016-hs-patsyns-ext.pdf
On Wed, Oct 6, 2021 at 10:23 AM Gergő Érdi wrote:
>
> > I'm afraid none of this is apparent from the User Guide -- and I even
> > contribute
