[GHC] #13218: <$ is bad in derived functor instances

[GHC]

#13218: <$ is bad in derived functor instances
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  deriving-perf
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by David Feuer <David.Feuer@…>):

 In [changeset:"2219c8cd612ec7920a3bd1661b3c663575737267/ghc" 2219c8c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2219c8cd612ec7920a3bd1661b3c663575737267"
 Derive <$

 Using the default definition of `<$` for derived `Functor`
 instance is very bad for recursive data types. Derive
 the definition instead.

 Fixes #13218

 Reviewers: austin, bgamari, RyanGlScott

 Reviewed By: RyanGlScott

 Subscribers: RyanGlScott, thomie

 Differential Revision: https://phabricator.haskell.org/D3072
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13218#comment:2>
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