[GHC] #870: extra commas accepted in import export lists

#870: extra commas accepted in import export lists
-------------------------+--------------------------------------------------
    Reporter:  ross      |        Owner:         
        Type:  bug       |       Status:  new    
    Priority:  normal    |    Milestone:         
   Component:  Compiler  |      Version:  6.4.2  
    Severity:  normal    |     Keywords:         
          Os:  Unknown   |   Difficulty:  Unknown
Architecture:  Unknown   |  
-------------------------+--------------------------------------------------
GHC accepts non-standard imports like
 {{{
 import M (,,foo,,,bar,,,)
 }}}
 creating problems for other Haskell implementations.  Ditto for exports.

 Suggest modifying this part of the grammar:
 {{{
 exportlist :: { [LIE RdrName] }
         :  exportlist ',' export                { $3 : $1 }
         |  exportlist ','                       { $1 }
         |  export                               { [$1]  }
         |  {- empty -}                          { [] }
 }}}
 to
 {{{
 exportlist :: { [LIE RdrName] }
         :  exportlist1 ','                      { $1 }
         |  exportlist1                          { $1 }
         |  {- empty -}                          { [] }

 exportlist1 :: { [LIE RdrName] }
         :  exportlist1 ',' export               { $3 : $1 }
         |  export                               { [$1]  }
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/870>
GHC <http://www.haskell.org/ghc/>
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