[GHC] #9902: Type family, pattern not matching

[GHC]

#9902: Type family, pattern not matching
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              Reporter:  erisco      |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
  (Type checker)                     |         Keywords:
            Resolution:  invalid     |     Architecture:  x86_64 (amd64)
      Operating System:  MacOS X     |       Difficulty:  Unknown
       Type of failure:  GHC         |       Blocked By:
  rejects valid program              |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by erisco):

 Thanks Simon I see the issue now.

 Sorry to be using the bug tracker as a Q&A rather than reporting real
 bugs. There seems to be a limited number of people with knowledge of type
 level programming on #haskell which is where I go for help. Also, it has
 been too easy to mistakenly apply familiarities seen at the value level
 and has resulted in much of the confusion. I was under the impression that
 the correct kinds for `:.:` would be inferred because a solution exists,
 rather than giving an error, but that does not appear to be the case then.
 Will inference generally happen from innermost to outermost without
 backtracking?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9902#comment:2>
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