[GHC] #1877: Change the meaning of -fextended-default-rules

[GHC]

#1877: Change the meaning of -fextended-default-rules
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    Reporter:  simonmar  |       Owner:             
        Type:  task      |      Status:  new        
    Priority:  normal    |   Milestone:  6.10 branch
   Component:  GHCi      |     Version:  6.8.1      
    Severity:  normal    |    Keywords:             
  Difficulty:  Unknown   |    Testcase:             
Architecture:  Unknown   |          Os:  Unknown    
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 Currently `-fextended-default-rules` applies to source code modules.  GHCi
 has the extended defaulting behaviour by default for expressions typed at
 the prompt, and there's no way to change that.

 We propose the following change: extended defaulting would only ever apply
 to expressions typed at the GHCi prompt, and it would be disabled with
 `-fno-extended-default-rules` (on by default).

 See also #1200, where `-fextended-default-rules` was introduced.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1877>
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