This behavior changed in 7.6 I believe. It used to be that type operators needed to start with a colon, but that restriction was dropped. The documentation is out of date. Ticket #11046 is about updating Template Haskell to match the new behavior, but it doesn't affect the core story of type operators in (non-Template) Haskell. The core story is actually quite simple: all non-reserved symbols are type *constructors*, not type *variables*.
I'll post a bug about the documentation, which needs to be fixed, indeed. Richard On Dec 10, 2015, at 10:58 AM, John Leo <l...@halfaya.org> wrote: > Thanks, that's helpful. Sounds like the situation is even more complicated > than I realized. It will be great if the documentation can be updated once > the behavior stabilizes. > > John > > On Thu, Dec 10, 2015 at 7:54 AM, Alexey Vagarenko <vagare...@gmail.com> wrote: > This ticket might be relevant https://ghc.haskell.org/trac/ghc/ticket/11046 > > 2015-12-10 20:51 GMT+05:00 John Leo <l...@halfaya.org>: > I sent this to haskell-cafe a little while ago but didn't get a response, so > I thought I'd try here. I'd guess this is a case of the GHC user guide > needing an update, but I'd like an expert opinion. > > --- > > According to sections 7.4.3 and 7.4.4 of the latest GHC documentation > https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/data-type-extensions.html > you can define (7.4.3) an infix type constructor as long as it begins with a > colon, for example > data a :*: b = Foo a b > > and furthermore (7.4.4) you can define an infix operator without having to > use a colon if you enable the TypeOperators extension: > data a * b = Foo a b > > However if I try the former without using TypeOperators I get this compiler > error in 7.10.2: > Illegal declaration of a type or class operator ‘:*:’ > Use TypeOperators to declare operators in type and declarations > > Using TypeOperators fixes this, but then * without colon also works so I > don't see the point of using colon anymore. > > My guess is this was some some kind of historical distinction which is no > longer valid and the documentation needs to be updated. Is this true, or am > I missing something? > > John > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
