[GHC] #8762: Panic involving unboxed tuples and phantom types

[GHC]

#8762: Panic involving unboxed tuples and phantom types
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        Reporter:  josef             |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc1
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by goldfire):

 I just took a look at this and ended up in deeper waters within the type-
 checker than where I feel comfortable. But I did discover that the bug
 persists with

 {{{
 {-# LANGUAGE UnboxedTuples #-}
 module Bug where

 data Ty a = Int

 bug :: () -> (# Ty a, () #)
 bug _ = (# Int, () #)

 main :: IO ()
 main = do
   let (# a, b #) = bug ()
   return ()
 }}}

 Note that there is no `undefined`, and the previous type synonym `Ty` has
 now become a datatype.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8762#comment:3>
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