Superclass Equality constraints cp FunDeps

Richard Eisenberg rae at
Sun Apr 30 19:45:34 UTC 2017

Documentation is just about always suboptimal -- but the best people to suggest concrete improvements are those who were confused to begin with. So, by all means, submit patches!

Some relevant discussion on this point is on

Currently, there is no extension for ~. It's enabled either by GADTs or TypeFamilies. I agree that this is not the best design, and the ticket above is a plan to fix it. Probably wouldn't take much more than someone with the will to make the changes!


> On Apr 30, 2017, at 3:35 PM, Brandon Allbery <allbery.b at> wrote:
> On Sun, Apr 30, 2017 at 3:31 PM, Richard Eisenberg <rae at <mailto:rae at>> wrote:
> > On Apr 30, 2017, at 6:37 AM, Anthony Clayden <anthony_clayden at <mailto:anthony_clayden at>> wrote:
> > Is that behaviour officially documented somewhere?
> Not that I can find. Documentation on functional dependencies is somewhat lacking. This may be because fundeps has received little love of late.
> Not just fundeps; the originally cited behavior of equality constraints could also stand to be documented. In fact, I'd noticed a few shortcomings in equality constraint documentation --- including the question of, are they always enabled, or are there particular extensions that enable them? And if so, should they also have their own extension that becomes implied by those other extensions? So it's not even just documentation.
> -- 
> brandon s allbery kf8nh                               sine nomine associates
> allbery.b at <mailto:allbery.b at>                                  ballbery at <mailto:ballbery at>
> unix, openafs, kerberos, infrastructure, xmonad <>
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