On Mon, 21 May 2018 at 11:23 AM, Carter Schonwald <redir...@vodafone.co.nz> wrote:
> indeed .. and we can reasonably say "lets deal with the bandaid in one go > by cleaning it up in the next standard" > Thanks Carter/Brandon, the reason for asking how we should go about the discussion was exactly: where/how are we going to maximise the chance of finding out what code is out there, and how disruptive any 'clean up' might be? Ghc has occasionally made breaking releases (not saying that's what we want to do), usually with some advance warning/deprecation period. And generally the Haskell community has accommodated that with understanding of the decision, to fix their code. > so what would the next gen look like? > > eg: fresh variables get the usual implicit forall at the front of the > type, and everything else either needs an explicit quantifier OR it refers > to the outer implicit quantified variable? > I wanted to avoid discussing 'next gen' in possibly-obscure/write-only mailing lists; and preferably get the discussion where posterity can see the reasoning/examination of options. "fresh variables get the usual implicit forall" is what happens now. (It's just that the User Guide explains it really badly -- I'm trying to fix that separately https://ghc.haskell.org/trac/ghc/ticket/15146 .) If the outer variable(s) are not explicitly forall-quantified, then even same-named variables count as fresh. IOW merely putting a `forall` can change the meaning of a program -- that's what causes the most confusion (judging by SO). The exception is variables bound in a pattern signature for an existentially-quantified data constructor: they *must* be fresh. This is hard for a reader to follow because the pattern signature with data constructor looks the same whether or not the constructor is existentially-quantified. What's worse a constructor might have a mix of existential and universal variables. AntC > On Sat, May 19, 2018 at 2:56 PM, Brandon Allbery <allber...@gmail.com> > wrote: > >> On Sat, May 19, 2018 at 7:32 AM, Anthony Clayden < >> anthony_clay...@clear.net.nz> wrote: >> >>> So the explanation I've seen for the current design is it was deliberately >>> idiosyncratic, to minimise any disruption to existing code. Then I'm asking >>> whether any of that code is still around? If not/if it's been re-factored >>> to use ScopedTypeVariables, then any tweak to the design could have a freer >>> hand. >>> >>> >> The reason there's no discussion about that is that nobody here has the >> ability to go hunt down every last piece of code in every public or private >> (think Standard Chartered, Facebook, etc.) code base and its current owner, >> and order them to "fix" it. You can't win that battle. >> >> -- >> brandon s allbery kf8nh sine nomine >> associates >> allber...@gmail.com >> ballb...@sinenomine.net >> unix, openafs, kerberos, infrastructure, xmonad >> http://sinenomine.net >> > >> _______________________________________________ >> Glasgow-haskell-users mailing list >> Glasgow-haskell-users@haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users >> >>
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