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

9 Feb 2014

      #8762: Panic involving unboxed tuples and phantom types
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       Reporter:  josef             |             Owner:
           Type:  bug               |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       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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 I ran into a bug involving unboxed tuples and the following piece of code
 is an attempt at isolating the problem:

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

 type Ty a = Int

 bug :: Ty a -> (# Ty a, () #)
 bug ty = (# ty, () #)

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

 It seems that the phantom type is necessary to trigger the bug.

 The bug is still present in 7.8rc1.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8762
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