> On Jun 29, 2019, at 11:48 AM, Carter Schonwald <carter.schonw...@gmail.com> > wrote: > > Phrased differently is a magic stand in for 0 ary sum and products ? > > Or do you mean how n-ary sum and product are the same structure when n=1?
No -- I just mean that 0 (that is, Void) is the identity for sums and 1 (that is, Unit) is the identity for products. Sorry if this wasn't clear! Richard > > Forgot to cc list. Pardon the double send :) > > On Mon, Jun 24, 2019 at 11:22 PM Richard Eisenberg <r...@richarde.dev > <mailto:r...@richarde.dev>> wrote: > I forget if I'm the contributor Ben mentions below, but regardless: NoExt is > used in two separate ways within GHC. It's used both as the extension of a > sum (new constructor) and the extension of a product (new field in a > constructor). But the identity for sum is different than the identity for > products. To me, it makes good sense for the NoExt used as a product > extension (new field) to have the 1 trivial inhabitant (thus forming the > identity for products), but the NoExt used as a sum extension (new > constructor) to have 0 inhabitants (thus forming the identity for sums). > Clearly, one of these will need a new name. > > Thanks, > Richard > > > On Jun 24, 2019, at 4:57 PM, Ben Gamari <b...@smart-cactus.org > > <mailto:b...@smart-cactus.org>> wrote: > > > > Hi Shayan, > > > > During code review a contributor asked about a TTG extension point. > > While answering his question I realized I didn't have a good explanation > > for why NoExt is inhabited; as far as I can tell it should rather be > > unhabited. > > > > If there is a reason for this then can you: > > > > 1. describe why this is so in #16863 [1] > > 2. open an MR documenting the reason in Note [Trees that Grow]. > > > > If not, perhaps we should consider changing it; the current state of > > things is a bit awkward. > > > > Cheers, > > > > - Ben > > > > > > [1] https://gitlab.haskell.org/ghc/ghc/issues/16863 > > <https://gitlab.haskell.org/ghc/ghc/issues/16863> > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs@haskell.org <mailto:ghc-devs@haskell.org> > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > <http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs> > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org <mailto:ghc-devs@haskell.org> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > <http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs>
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