[GHC] #13474: GHC HEAD regression: Prelude.!!: index too large

[GHC]

#13474: GHC HEAD regression: Prelude.!!: index too large
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 Just took a look. The problem is that we're trying to make a `NthCo 0 g`
 where one of `g`'s types is `Constraint`. Of course, `Constraint` is
 identical to `TYPE LiftedRep`, so using `NthCo` is sensible, but GHC gets
 confused.

 I haven't tested it, but I'm nearly positive that merging Phab:D3316 would
 fix this. That patch is held up on discussions in #11715. It all boils
 down to a design question, and I don't feel like the discussion there has
 settled toward any consensus.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13474#comment:4>
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