[GHC] #9805: Use TrieMaps to speed up type class instance lookup

[GHC]

#9805: Use TrieMaps to speed up type class instance lookup
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        Reporter:  ezyang            |                   Owner:  ezyang
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.9
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by simonpj):

 If we need the keys, then yes, class `TrieKeyMap` looks good.  But I'm not
 yet certain that we do.  I need to look at your straw-man `TrieMap.hs`.

 See #9960 for an orthogonal issue that also concerns `TrieMap`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9805#comment:3>
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