Re: [GHC] #14420: Data families should not instantiate to non-Type kinds

5 Nov 2017

      #14420: Data families should not instantiate to non-Type kinds
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by Iceland_jack):

 * cc: Iceland_jack (added)

Comment:

 Hope this won't affect #12369,

 interestingly your
 [https://repository.brynmawr.edu/cgi/viewcontent.cgi?article=1075&context=compsci_pubs
 Constrained Type Families] paper doesn't mention constraining data
 families..

 But if we require all data families to be associated

 {{{#!hs
 class CAny k where
   data Any :: k
 }}}

 then using `Any :: Bool` as a case in the type family `F` will create a
 `CAny Bool` constraint, we are already barred from actually defining `data
 instance Any :: Bool`.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14420#comment:1
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