[GHC] #8171: Extending ExtendedDefaultRules

[GHC]

#8171: Extending ExtendedDefaultRules
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        Reporter:  ekmett            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.3
      Resolution:                    |             Keywords:
                                     |  ExtendedDefaultRules
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #2641             |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by crockeea):

 * cc: ecrockett0@… (added)


Comment:

 Also see #12271. My primary concern there is GHC rather than GHCi. My main
 point there is: users should be able to specify defaults for user-defined
 /non-Prelude constraints; defaulting should not be a magical property
 baked into specific Prelude typeclasses.

 It sounds like the solution proposed here would require -XEDR, whereas my
 proposed solution just modifies the existing `default` tuple, similar to
 what Edward suggested at the end of
 [https://ghc.haskell.org/trac/ghc/ticket/8171#comment:4 comment 4]. I
 think removing rule 3 from the EDRs would effectively remove the "magic"
 that I talk about in that ticket.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8171#comment:13>
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