Re: Show, Eq not necessary for Num [Was: Revamping the numeric classes]

Marcin 'Qrczak' Kowalczyk wrote:

Sat, 10 Feb 2001 14:09:59 +1300, Brian Boutel pisze:

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Can you demonstrate a revised hierarchy without Eq? What would happen to Ord, and the numeric classes that require Eq because they need signum?

signum doesn't require Eq. You can use signum without having Eq, and you can sometimes define signum without having Eq (e.g. on functions). Sometimes you do require (==) to define signum, but it has nothing to do with superclasses.

Let me restate my question more carefully: Can you demonstrate a revised hierarchy without Eq? What would happen to Ord and the numeric classes with default class method definitions that use (==) either explicitly or in pattern matching against numeric literals? Both Integral and RealFrac do this to compare or test the value of signum. In an instance declaration, if a method requires operations of another class which is not a superclass of the class being instanced, it is sufficient to place the requirement in the context, but for default class method definitions, all class methods used must belong to the class being defined or its superclasses. --brian