[GHC] #11348: Local open type families instances ignored during type checking

[GHC]

#11348: Local open type families instances ignored during type checking
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        Reporter:  alexvieth         |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc1
      Resolution:  fixed             |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  typecheck/should_compile/T11348
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1762
       Wiki Page:                    |
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Comment (by goldfire):

 Hooray Hooray Hooray! Thanks, Alex! This was a major engineering task that
 I shuddered at the thought of. It has lightened my day knowing that I
 won't have to do this. :)

 If that was fun for you, the next step is to support
 [https://en.wikipedia.org/wiki/Induction-recursion_%28type_theory%29
 induction recursion]. I'm pretty sure I know how to do this, but it will
 take a similar engineering effort. It's not for the faint of heart, but
 this patch shows that your heart is not faint. As an added bonus,
 supporting induction recursion in GHC may be enough to publish a paper
 about, if that kind of thing is an incentive for you. Some notes (meant
 for myself, YMMV) I have on the subject are
 [https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell/Internal#Separatingtypesignaturesfromdefinitions
 here].

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11348#comment:17>
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