[GHC] #5998: GHCi's :info to return all the visible instances, not just the ones imported from currently loaded files

[GHC]

#5998: GHCi's :info to return all the visible instances, not just the ones
imported from currently loaded files
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    Reporter:  errge             |       Owner:                  
        Type:  feature request   |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  GHCi              |     Version:  7.4.1           
    Keywords:  ghci :info        |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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Changes (by simonpj):

  * difficulty:  => Unknown


Comment:

 Currently this is by design: GHC only displays instances whose types have
 been brought into scope.  In this case module B does not export the type
 C, so C is not in scope in Main, so its instances are not displayed.

 This is a design choice (implemented in the `plausible` function in
 `InteractiveEval.getInfo`).  I'm not sure when we introduced it, or how
 persuasive the reasoning was at the time.  Changing it to display all
 instances would be easy; but then you might get `Eq` instantces displayed
 for zillions of types that you had no interest in.

 One could make other choices: eg display only for types in the current
 package, not for imported packages... I don't know what's best.  Opinions
 anyone?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5998#comment:1>
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