FWIW. Often when I encounter that error, I want `ScopedTypeVariables`, yet my code doesn’t always has the scoped type variable used. So even GHC could parse further and propose it to me, there isn’t anything from to do it :(
I don’t know if many use /just/ `ExplicitForAll`... - Oleg > On 11 Aug 2016, at 20:30, Karolina Drobnik <[email protected]> wrote: > > Hello everyone, > > I am working on my first ticket (#11669, linked below) > and I have some doubts after a little bit of hacking. > > There was a hint that an error message should be > changed from the one suggesting RankNTypes to ExplicitForall. > In my opinion it would be quite confusing for the user, especially where > the type is ill-formed. A plain parse error should be shown here. > > It is clear that it should be done in such a way after turning on one > of the extensions, but what about the situation where proposed > fix (suggesting RankNTypes/ExplicitForall) won't work? > We should be able to distinguish ill-formed type from the correct one, > even before the extension activation. To be honest - I don't know how to do > it. > > Additionally, I am not sure if we can assume that an user wants > to use arbitrary rank (which implies ExplicitForall) or just a forall keyword. > I am for the second one, but it is just my assumption. > > And the last minor thing - a type formed in this way also rises an error > suggesting using RankNTypes (as we know that wouldn't solve the problem): > > f :: a. -> Int > f = undefined > > Maybe we could treat it as a typo (simple parse error) and propose > an extension activation only when forall was parsed earlier? > That could be tricky. > > I'd appreciate some thoughts on this issue because I felt a bit lost > after digging around the parser. > > Best regards, > > Karolina > --------------------------------------------------------- > #11669 - https://ghc.haskell.org/trac/ghc/ticket/11669 > <https://ghc.haskell.org/trac/ghc/ticket/11669> > _______________________________________________ > ghc-devs mailing list > [email protected] > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
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