Re: [GHC] #13985: GHC 8.0 regression: ‘k’ is not in scope during type checking, but it passed the renamer

[GHC]

#13985: GHC 8.0 regression: ‘k’ is not in scope during type checking, but it passed
the renamer
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13738            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I was hoping to nab this in a drive-by fix, but that didn't happen. The
 solution here, I think, is to put the kind variables in the implicit part
 of the `dfid_pats` field. (This is rather like what happens with ordinary
 data declarations.) Then, they'll be in scope during type-checking and we
 can discover that they're "floating".

 There's an interesting invariant that data instance declarations violate:
 every `Name` invented by the renamer must be bound precisely once. Indeed
 the "not in scope during type checking" error says the invariant is not
 upheld. It makes me want a linear type system, but we can't always get
 what we want.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13985#comment:2>
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