[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 ezyang):

 Some clarifying comments from the Skype conversation:

 1. The reason why the first prototype doesn't make sense was because I
 accidentally thought the template variables were in the expression I was
 matching with, rather than in the *keys* of the TrieMap. This was also why
 I believed a key was necessary.

 2. TyBox in the prototype is a hack to avoid having circularity when
 specifying the kind of box. We don't really need kinds for the prototype
 but I was trying to keep the data structures as close as possible to GHC
 proper.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9805#comment:6>
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