[Haskell-cafe] Why is Bool no instance of Num and Bits?

John Meacham john at repetae.net
Wed Jun 24 08:13:06 EDT 2009

On Fri, May 08, 2009 at 04:36:41PM +0200, Stephan Friedrichs wrote:
> When looking for an xor function, I found one in Data.Bits but couldn't
> use it for Bool, because Bool is no instance of Bits and of Num (which
> would be necessary, because it's "class (Num b) => Bits b"). My question
> is: Why not?

This has bothered me too. However, I think the root problem is that
'Num' is a superclass of 'Bits'. There is no reason it should be, all
the default instances can be specified without the Num dependency.



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