Proposal: Remove Show and Eq superclasses of Num

Yitzchak Gale gale at
Sun Sep 18 11:19:06 CEST 2011

+1 on removing the Show constraint.
I abstain on the Eq constraint - either way is fine with me.

Jon Fairbairn wrote:
> But pattern matching for Double or Float is a Bad Thing, so
> wouldn’t the solution to this be to put the EQ constraint
> somewhere else, such as Integral where it would be less
> improper?

The Badness comes from the Eq instance itself. Once that
instance exists, using it for pattern matching isn't any worse
than equating with a Num literal in an expression. If we are
going to have an Eq constraint at all, it might as well be on


More information about the Libraries mailing list