If this is just about GHC internals, then by all means carry on. -Edward
On Wed, Dec 29, 2021 at 12:19 PM Edward Kmett <ekm...@gmail.com> wrote: > Please no. > > I use them to pun constructors between multiple types that will be in > scope at the same time, (e.g. when I have 8 Var constructors on different > types in scope between my core language term language and type language...) > and often overload them on classes. I can't write the pragma, and the PS_ > destroys any utiity I get from any common name. > > I use them as a migration guide, when I add functionality. PS_ destroys > that usecase, but then COMPLETE pragmas are a hacky mess in their current > state and often simply can't be applied. > > All the existing pattern constructors in the lens library would fail > either bar. > > So I have to say, either of these would probably destroy *every* use of > pattern synonyms I use today. > > -Edward > > On Wed, Dec 29, 2021 at 11:55 AM Richard Eisenberg <li...@richarde.dev> > wrote: > >> Hi devs, >> >> Maybe I'm just old fashioned, but I've come to find pattern synonyms >> really confusing. Because pattern synonyms will tend to appear next to >> proper data constructors in code (and they look just like data >> constructors), when I see one, I think it *is* a data constructor. This >> problem was motivated by a recent MR that introduces a new pattern >> synonym >> <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/7261/diffs#7dcf5b567a6cd3c9d98cf8d57323fbca1b1536e9_1128_1130> >> that >> caught me off-guard. >> >> So, I'd like to propose the following convention: Every pattern synonym >> satisfies one of the following two criteria: >> 1. The pattern synonym is a member of a set of synonyms/constructors that >> expresses a view of a type. There would naturally be a `COMPLETE` pragma >> including the set. `GHC.Types.Var.Inferred` is an example. >> 2. The pattern synonym begins with the prefix `PS_`. >> >> In the end, I'd probably prefer just (2). With Inferred, for example, >> I've been caught in the past trying to figure just what the constructors of >> ArgFlag were (there seemed to be too many), until I realized what was going >> on. >> >> Pattern synonyms are useful abstractions. I like them. But my mental >> model of a pattern match is that it matches the structure of the scrutinee >> and performs no computation. Pattern synonyms violate both of these >> assumptions, and so (as a reader) I like to know when to put these >> assumptions to the side. >> >> Future IDE support that could, say, color pattern synonyms differently to >> regular constructors would obviate the need for this convention. >> >> What do others think here? `PS_` is ugly. I don't need something quite so >> loud and ugly, but it's also easy to remember and recognize. >> >> Thanks! >> Richard >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs@haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >> >
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