Re: Arrow Classes

On Tue, Jul 15, 2003 at 01:07:12AM -0700, Ashley Yakeley wrote:

In article <200307141536.39157.qrczak@knm.org.pl>, Marcin 'Qrczak' Kowalczyk wrote:

...

It doesn't provide instances of Num for anything which is already an instance of the other classes. And in Haskell 98 they must be defined separately for each type, instance (...) => Num a doesn't work.

It works in extended Haskell however, so I suspect it lays to rest the question of needing some other language extension.

I disagree! This method (putting each function in its own class) does not address two related points: a) Being able to declare default values for a method declared in a superclass; b) Being able to refine a type heirarchy without the users noticing (and without explosion of the number of instance declarations required). Peace, Dylan