IIRC ConstraintKinds is only required in the module that defines the type synonym, so your module T does not need it. My guess is that haskell-src-exts sees 'Log.Stack =>', in which we have nullary constraint instead of a unary constraint, and assumes that's bogus without MultiParamTypeClasses. But I'm not familiar with haskell-src-exts' internals, so that's just a wild guess :)
FYI, as of RC2 we provide a type synonym type HasCallStack = (?callStack :: CallStack) in GHC.Stack, which is the recommended way to request a CallStack. We're hiding the implicit parameter from the docs and API, as the reliance on using the same name is a bit of a misfeature. We might also reimplement HasCallStack without implicit-params in the future, so in the interest of forward-compatibility I'd suggest using HasCallStack instead of your own implicit-parameters. Eric On Sun, Feb 14, 2016, at 16:32, Evan Laforge wrote: > I recently upgraded to ghc 8 and started using stacks via > ImplicitParams. For that I wind up using 'type Stack = (?stack :: > CallStack)' and so ContraintKinds (I see that in the future GHC will > do this by default). > > So now I can have a file like: > > module T where > import qualified Log as Log > > f :: Log.Stack => IO () > f = Log.warn "blah blah" > > I noticed that now haskell-src-exts refuses to parse this file, saying > 'MultiParamTypeClasses language extension is not enabled.'. > > I assume it's a bug with haskell-src-exts in that it should require > LANGUAGE ConstraintKinds instead, but then GHC itself doesn't want > ConstraintKinds. Instead, it wants FlexibleContexts. From the docs, > FlexibleContexts seems to be about the contexts in instance heads. > > Is this intentional? I'll go ahead and make a bug for > haskell-src-exts, but the ghc behaviour here seems odd as well. What > extension should haskell-src-exts require to parse this? > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
