[GHC] #12709: GHC panic

[GHC]

#12709: GHC panic
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        Reporter:  Iceland_jack      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Btw this works,

 {{{#!hs
 data BoxUnbox = BUB Int Int#

 a :: (forall rep (a :: TYPE rep). Num a => a) -> BoxUnbox
 a u = BUB u u
 }}}

 as does this

 {{{#!hs
 b :: BoxUnbox
 b = do
   let u :: forall rep (a :: TYPE rep). Num a => a
       u = 24
   BUB u u
 }}}

 and it looks like it fails on more complicated numerical equations

 {{{#!hs
 --   × × × FAILS × × ×
 a_applied :: BoxUnbox
 a_applied = a (1 + 2 + 3)

 --   × × × FAILS × × ×
 b' :: BoxUnbox
 b' = do
   let u :: forall rep (a :: TYPE rep). Num a => a
       u = 1 + 2 + 3
   BUB u u
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12709#comment:1>
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