[GHC] #13893: Improved Help for Control.Concurrent and Control.Exception when "variable not in scope"

[GHC]

#13893: Improved Help for Control.Concurrent and Control.Exception when "variable
not in scope"
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        Reporter:  vanto             |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Poor/confusing    |  Unknown/Multiple
  error message                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by vanto):

 Here I am talking about library that are natively in the compiler, of
 course, such as
 {{{Data.Char}}}.
 The principle would be identical to the suggestion of the pragmas to be
 used which are stated in the error message by the compiler.\\
 This does not apply to library that are external to the compiler.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13893#comment:1>
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