Thu, 08 Feb 2001 15:11:21 +0100 (CET), Elke Kasimir
However, what is missing for me is something like:
type Comfortable a = (Show a, Eq a, Num a) => a
or
class (Show a, Read a, Eq a) => Comfortable a instance (Show a, Read a, Eq a) => Comfortable a
I agree and think it should be easy to add. The latter syntax is nice: obvious what it means, not legal today. This instance of course conflicts with any other instance of that class, so it can be recognized and treated specially as a "class synonym".
For Haskell, I could imagine (without having having much thought about) in addition to the things mentioned in the beginning, several things making supporting the "locally, fast and easy", including a mean to define classes with implied memberships, for example declarations saying that "Foo is the class of all types in scope for which somefoo :: ... is defined", or declarations saying that "class Num is locally restricted to all instances of global Num which also belong to Eq".
Here I would be more careful. Don't know if local instances or local classes can be defined to make sense, nor if they could be useful enough... -- __("< Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK