[GHC] #14547: Wrong warning by -Wincomplete-patterns

[GHC]

#14547: Wrong warning by -Wincomplete-patterns
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        Reporter:  YoshikuniJujo     |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  incomplete-
                                     |  patterns OverloadedLists,
                                     |  PatternMatchWarnings TypeFamilies
Operating System:  Linux             |         Architecture:  x86
 Type of failure:  Incorrect         |            Test Case:
  error/warning at compile-time      |  deSugar/should_compile/T14547
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4624
       Wiki Page:                    |
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Comment (by simonpj):

 > Indeed we don't need to know the toList of [] instance is identity
 function,

 Good point. So this ticket is

 * not about overloaded strings
 * not about type functions

 It's only about view patterns.  Could you re-formulate the example to
 eliminate the unnecessary clutter, and focus just on view patterns?

 And then (sorry to be slow) take us more slowly through what the problem
 is? It'll be something to do with the way that the pattern match checker
 deals with view patterns, I guess.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14547#comment:5>
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