
All yays from committee members please reply with yes to
Anthony, this proposal is to remove the Eq and Show constraints from the
Num class. Specific instances of Num, like Int and Float, will still have
those instances. This has been how it is in GHC for a long time now, so it
really is a matter for the Haskell' committee rather than one of the GHC
committees.
The motivation is that there are many types with sensible definitions for
addition and multiplication etc that can't be instances of Eq or Show, for
example functions to numbers (allowing us to write "sin + cos" instead of
"\x -> sin x + cos X") or arbitrary real numbers (where comparison isn't
necessarily computable).
I'm not sure why this is being discussed on the mailing list rather than
the Github proposals thing, but I do know that that has grown somewhat
inactive and this is as good as anything for getting the Haskell' committee
to make a final judgement.
Nathan
On 8 Sep 2017 8:35 am, "Anthony Clayden"