[Haskell-cafe] ordNub
Atze van der Ploeg
atzeus at gmail.com
Thu Jan 1 14:37:09 UTC 2015
Your question is if I understand correctly, whether we can think of a type
that has a law abiding Eq instance that gives equality as fine grained as
extensional equality (meaning structural equality?) but for which no law
abing instance of Ord can be given such that a <= b && a >= b ==> a == b
This boils down to the question whether on each set with an equality
relation defined on it a total ordering (consistent with the equality
relation) can also be defined. One counterexample is the complex numbers.
Does that answer your question?
Cheers!
On Jan 1, 2015 3:27 PM, "Tom Ellis" <
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:
> On Thu, Jan 01, 2015 at 03:22:55PM +0100, Atze van der Ploeg wrote:
> > > i want it to be at least as fine grained as extensional equivalence
> >
> > Then see Oleg's comment or am i missing something here?
>
> Perhaps you could explain Oleg's comment. I don't understand it.
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