[GHC] #13297: Panic when deriving Applicative instance through transformer

[GHC]

#13297: Panic when deriving Applicative instance through transformer
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        Reporter:  blaze             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"713ebd7cf03876c6bedc1be9fba8f60ccc5bc8f0/ghc" 713ebd7/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="713ebd7cf03876c6bedc1be9fba8f60ccc5bc8f0"
 Fix computation of dfun_tvs in mkNewTypeEqn

 This bug was causing Trac #13297.

 We were recomputing ds_tvs, and doing it wrongly (by omitting
 variables that appear only in mtheta).  But actually plain 'tvs'
 is just fine.  So code deleted, and bug fixed.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13297#comment:1>
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