> From: Casey McCann <c...@uptoisomorphism.net> > <CAJ5riwLLu=wAFXm8VPnqRG2Daxxgf=upgxzchydmebgngix...@mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > On Tue, Sep 20, 2011 at 8:20 PM, Daniel Fischer > <daniel.is.fisc...@googlemail.com> wrote: > >> However, nowadays I tend to think that making the Eq and Ord instances >> well-behaved (wrt the class contract) and having separate IEEE comparisons >> would overall be preferable. >> There is still the question whether all NaNs should be considered equal or >> not [and where Ord should place NaNs]. > > IEEE semantics are incompatible with Ord regardless. The problem can > be fixed by changing Ord, removing the instance completely, or > changing the instance to ignore the IEEE spec. I think the latter is > the least bad option in the big picture. > > I still don't see why it makes sense to add separate IEEE comparisons > instead of just adding a standard partial order class, though. Surely > posets are common enough to justify the abstraction, and it surprises > me that one isn't already included. No doubt there are at least three > or four different partial ordering classes on Hackage already.
I agree with this already, and will agree more strongly if ConstraintKinds become widely available. > >> Google suggests "Exception for NaN" from May. > > Ah, yes, wherein someone suggested that comparing to NaN should be a > runtime error rather than give incorrect results. A strictly more > correct approach, but not one I find satisfactory... I would consider this better than the current situation. At least your sets wouldn't be silently corrupted. John L. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
