[GHC] #4047: Incorrect unused-import warning in ghci

[GHC]

#4047: Incorrect unused-import warning in ghci
------------------------------------------------+---------------------------
  Reporter:  Berengal                           |          Owner:                  
      Type:  bug                                |         Status:  closed          
  Priority:  normal                             |      Milestone:                  
 Component:  GHCi                               |        Version:  6.12.1          
Resolution:  worksforme                         |       Keywords:                  
Difficulty:                                     |             Os:  Unknown/Multiple
  Testcase:                                     |   Architecture:  Unknown/Multiple
   Failure:  Incorrect warning at compile-time  |  
------------------------------------------------+---------------------------
Changes (by simonpj):

  * status:  new => closed
  * resolution:  => worksforme


Comment:

 I believe you may be misled by two things:

  * `ghc --make` does not recompile things that have already been compiled,
 and that can lead to lack of warnings if you do `ghc --make` right after
 (say) your `ghci` run.  Try adding `-fforce-recomp`

  * `undefined` is not a keyword: it is simply a named definition that is
 indeed imported from the Prelude. So there really is a difference between
 `[]` and `undefined` on the RHS of your definition.

 Everything seems to be working fine to me.  If you still thing there's a
 bug, by all means re-open this.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4047#comment:1>
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