Thanks for the feedback, everyone! I've typed up the developments so far in the DerivingStrategies Haskell wiki page [1].
Here's what seems to be the consensus: * The syntax in which actual keywords are used to designate deriving strategies was the clear favorite. * In particular, a slight edge goes to the form in which multiple deriving clauses can be placed after a datatype, and each `deriving` clause has its own (optional) strategy keyword, as opposed to putting the keyword directly in front of the derived type. * The `builtin` keyword was poorly received. There isn't a obvious candidate to replace it, and several of us like the word `bespoke`, so it looks like `bespoke` will be the replacement. (If someone ends up complaining about it, we've got several other choices.) Any other questions or comments? Ryan S. ----- [1] https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/DerivingStrategies On Mon, Jul 18, 2016 at 5:54 PM, Simon Peyton Jones <simo...@microsoft.com> wrote: > I'm not following all the details here, and I do not feel strongly about > syntax; but I do hope that you'll update the wiki page to reflect the > discussion. > > Thanks > > Simon > > -----Original Message----- > From: ghc-devs [mailto:ghc-devs-boun...@haskell.org] On Behalf Of Ryan Scott > Sent: 18 July 2016 15:00 > To: Richard Eisenberg <e...@cis.upenn.edu> > Cc: Andres Loeh <m...@andres-loeh.de>; GHC developers <ghc-devs@haskell.org> > Subject: Re: Request for feedback: deriving strategies syntax > > Andres, > >> The objects probably shouldn't be type synonyms, but they could be >> special datatypes or type families, perhaps. > > I considered that - we already have some special datatypes, type families, > and type classes currently. However, neither datatypes nor type families are > allowed to appear as the outermost type in an instance declaration (unless we > bake in a very prominent exception to this rule), and if we imbued type > classes with this magic, one might think that "deriving (GND Eq)" means we're > deriving an instance for the magical GND class, not Eq. So those approaches > don't sound satisfying to me on a cursory examination. > > Richard, > >> The one idea I can suggest in this space (somewhat tongue-in-cheek, >> but feel free to take it seriously) is `bespoke` > > It might be a tongue-in-cheek suggestion, but I _really_ like it. It captures > the intended semantics better than any other previous suggestion, I think. > And we're already going to be appropriating a new keyword with "anyclass", so > why not take "bespoke" as well? :) > > Please stop me if I've slipped into madness here. > >> I thought about verbosity here, and it's not clear which one is more >> verbose. For example, I frequently define a new newtype and then wish to use >> GND to derive a whole host of instances. In this case (is it common?), >> `deriving (X, Y) deriving newtype (A,B,C,D,E,F)` is shorter than putting >> newtype on each class name. > > That's a good point. Another thing to consider is that I suspect in 90% of > the time, users are only going to be reaching for -XDerivingStrategies in the > scenario when they enable both -XGeneralizedNewtypeDeriving and > -XDeriveAnyClass. That will happen when they want to derive instances for > newtypes, and as you said, you typically derive several instances at a time > when defining newtypes. > Therefore, it seems less noisy to factor out the deriving strategy names so > that readers can tell at a glance which batch of instances are > newtype-derived and which are anyclass-derived, instead of having to read a > keyword before every single type. > > Plus, on a superficial level, I like keeping the deriving strategy name > outside of the parentheses. I think it makes clear that these keywords aren't > modifying the type we're deriving, only the means by which we're deriving it. > Of course, you may feel differently than I do, so please speak up if you > disagree! > > > Ryan S. > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.haskell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc-devs&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7cea562a7e9e494f07cede08d3af13cbc7%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=rKTWOkEZsKUdDOTnk7WL2BNx1lf36uelef4JDg0pX44%3d _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
