relaxing instance declarations
batterseapower at hotmail.com
Mon Apr 29 23:41:41 CEST 2013
You could probably get away with just using two "where" clauses:
instance Foo a where
bar = ...
auxilliary = ...
On 28 April 2013 18:42, Edward Kmett <ekmett at 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 <doug at 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 <ekmett at 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 <doug at cs.dartmouth.edu
> >> 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
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> Haskell-prime at haskell.org
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