[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
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        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15076            |  Differential Rev(s):  Phab:D4769
       Wiki Page:                    |
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Comment (by goldfire):

 I have two takeaways from this:

 - An accumulator style is the Right Way to go when building up a set. This
 idea should probably be abstracted over right in the `VarSet` interface.
 But do we get these gains without eta-expanding everything? (See Note [FV
 eta expansion] in FV.)

 - The extra work to track order has no effect. I find this surprising, but
 not overly so, because we can avoid the extra work via laziness.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:94>
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