Proposal: Remove Show and Eq superclasses of Num

Jon Fairbairn jon.fairbairn at
Sun Sep 18 10:54:52 CEST 2011

Malcolm Wallace <malcolm.wallace at> writes:

>> The first 2 attached patches (for base and ghc respectively) remove the
>> Show constraint. I'm not aware of any justification for why this
>> superclass makes sense.
> I'm strongly in favour of removing the Show constraint.
>> The next 2 patches (for base and unix respectively) remove the Eq
>> constraint. Here's there's some justification in the superclass, as it
>> makes
>>    f 5 = ...
>> work for any Num type, rather than also needing an Eq constraint,
> I am undecided whether removing the Eq constraint is a good
> thing or not. In principle, yes, it makes perfect sense. But
> in practice, the example you give of pattern-matching a
> literal now requiring an Eq context, smells slightly wrong to
> me.

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

Jón Fairbairn                                 Jon.Fairbairn at

More information about the Libraries mailing list