[GHC] #7624: Handling ImplicitParams in Instance Declaration

[GHC]

#7624: Handling ImplicitParams in Instance Declaration
------------------------------+---------------------------------------------
Reporter:  philipjf           |          Owner:                  
    Type:  bug                |         Status:  new             
Priority:  normal             |      Component:  Documentation   
 Version:  7.6.1              |       Keywords:  ImplicitParams  
      Os:  Unknown/Multiple   |   Architecture:  Unknown/Multiple
 Failure:  Documentation bug  |      Blockedby:                  
Blocking:                     |        Related:                  
------------------------------+---------------------------------------------
 The  GHC documentation states that ImplicitParam's may not be used in
 class or instance declaration constraints.   see for example
 http://www.haskell.org/ghc/docs/7.6.1/html/users_guide/other-type-
 extensions.html In practice though, at least on the Mac, all recent
 version of GHC have permitted such instances.  At the very least the
 documentation should make clear that the compiler might permit such
 instances, but they have undefined behaviour.  Ideally, these would simply
 be permitted.

 [http://joyoftypes.blogspot.com/2013/01/using-compiler-bugs-for-fun-and-
 profit.html Why I think the (undocumented) current behavior is correct]

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7624>
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