[GHC] #12605: UnboxedSums causes parse error on hash operator e.g. `let (#) = (+)`

[GHC]

#12605: UnboxedSums causes parse error on hash operator e.g. `let (#) = (+)`
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           Reporter:  jberryman      |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
 GHCi, version 8.1.20160920: http://www.haskell.org/ghc/  :? for help
 Prelude> let (#) = (+)
 Prelude> :set -XUnboxedSums
 Prelude> let (#) = (+)

 <interactive>:3:7: error: parse error on input ‘)’
 }}}

 I first noticed this in an import statement:


 {{{
 import Data.Functor.Utils (Max(..), Min(..), (#.))
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12605>
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