Re: Re[2]: overlapping instances and constraints

On 2/28/06, Bulat Ziganshin wrote:

Tuesday, February 28, 2006, 1:54:25 PM, you wrote: CR> class NEq a b CR> instance Fail a => NEq a a CR> instance NEq a b

i think that this definition just use ad-hoc overlapping instances resolution mechanism that we want to avoid :)))

Actually, it illustrates beautifully why ad-hoc overlapping doesn't work. There are two interpretations, the desired one, and one that just ignores the the first and uses the second for everything. -- Taral "Computer science is no more about computers than astronomy is about telescopes." -- Edsger Dijkstra