[GHC] #15720: Assign to literals is allowed in ghci

[GHC]

#15720: Assign to literals is allowed in ghci
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        Reporter:  sighingnow        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by sighingnow):

 Should we enable `-Wunused-pattern-binds` by default ?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15720#comment:2>
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