Max's idea (see below) of a second where clause is cute, but not sanctioned by Haskell syntax.
Iavor wrote, "It would be quite arbitrary to restrict this only to instances." Actually what I have in mind is to make the language MORE consistent, by eliminating distinctions between instance-wheres and ordinary declaration-wheres. Currently instance-wheres may only declare class methods, while declaration-wheres may declare variables at will. Also instance-wheres may not declare type signatures, while declaration-wheres may. I propose dropping these restrictions on instance-wheres. Hazard: Adding a method to an existing class could accidentally capture a name that was previously local to an instance-where. Capture can be prevented by declaring type signatures for local variables. The compiler might warn when such defensive declarations are lacking. Doug On Mon, 29 Apr 2013 15:56 Iavor Diatchki <iavor.diatc...@gmail.com> wrote Hello, I think that if we want something along those lines, we should consider a more general construct that allows declarations to scope over other declarations (like SML's `local` construct). It would be quite arbitrary to restrict this only to instances. -Iavor On Mon, Apr 29, 2013 at 2:41 PM, Max Bolingbroke <batterseapo...@hotmail.com > wrote: > You could probably get away with just using two "where" clauses: > > instance Foo a where > bar = ... > where > auxilliary = ... > > > > > On 28 April 2013 18:42, Edward Kmett <ekm...@gmail.com> wrote: > >> Makes sense. I'm not sure what a good syntactic story would be for that >> feature though. Just writing down member names that aren't in the class >> seems to be too brittle and error prone, and new keywords seems uglier than >> the current situation. >> >> Sent from my iPad >> >> On Apr 28, 2013, at 1:24 PM, Doug McIlroy <d...@cs.dartmouth.edu> wrote: >> >> > Not always. For example, you can't mess with the declaration >> > of a standard class, such as Num. >> > >> > On Sun, Apr 28, 2013 at 12:06 PM, Edward Kmett <ekm...@gmail.com> >> wrote: >> > >> >> You can always put those helper functions in the class and then just >> not >> >> export them from the module. >> > >> > On Sun, Apr 28, 2013 at 10:49 AM, Doug McIlroy <d...@cs.dartmouth.edu >> >wrote: >> > >> >> Is there any strong reason why the where clause in an instance >> >> declaration cannot declare anything other than class >> >> operators? If not, I suggest relaxing the restriction. >> >> >> >> It is not unusual for declarations of class operators to >> >> refer to special auxiliary functions. Under current rules >> >> such functions have to be declared outside the scope in >> >> which they are used. >> >> >> >> Doug McIlroy >> >> _______________________________________________ >> Haskell-prime mailing list >> Haskell-prime@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-prime >> >> > > _______________________________________________ > Haskell-prime mailing list > Haskell-prime@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-prime > > Content-Type: text/html; charset=UTF-8 _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
