[GHC] #11572: BangPatterns-related behavior regressions on GHC 8.0

[GHC]

#11572: BangPatterns-related behavior regressions on GHC 8.0
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc2
      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 RyanGlScott):

 Another strange facet of the GHCi portion of the bug: the behavior is
 different depending on whether a wildcard or a named type variable is
 used. Here's another bizarre error you can get in GHCi (but not compiled
 code):

 {{{
 λ> :set -XMagicHash -XBangPatterns
 λ> import GHC.Prim
 λ> let !a = (undefined :: Int#) in print 2

 <interactive>:3:5: error:
     • You can't mix polymorphic and unlifted bindings
         !a = (undefined :: Int#)
         Probable fix: add a type signature
     • In the expression: let !a = (undefined :: Int#) in print 2
       In an equation for ‘it’:
           it = let !a = (undefined :: Int#) in print 2
 }}}

 This works without issue in GHCi 7.10.3.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11572#comment:1>
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