[GHC] #10547: feature request: expanding type synonyms in error messages

[GHC]

#10547: feature request: expanding type synonyms in error messages
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        Reporter:  osa1              |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  typecheck/should_fail/ExpandSynsFail1,2,3,4
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1016
       Wiki Page:                    |
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Comment (by sjcjoosten):

 Attached script is a reason to not have it on by default. The example code
 takes long enough to notice a delay but still see a result; changing the
 T12 and S12 into something like T15 S15 makes it take 'forever'. I don't
 know if this will occur in practice – it's hard to measure since all of
 hackage seems to type-check, but it's a reason to keep the switch off by
 default (as it is in rc-4).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10547#comment:13>
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