[GHC] #1826: unable to list source for <exception thrown> should never occur

[GHC]

#1826: unable to list source for <exception thrown> should never occur
--------------------------------+-------------------------------------------
    Reporter:  guest            |       Owner:         
        Type:  feature request  |      Status:  new    
    Priority:  normal           |   Milestone:         
   Component:  Compiler         |     Version:  6.8.1  
    Severity:  normal           |    Keywords:         
  Difficulty:  Unknown          |    Testcase:         
Architecture:  Unknown          |          Os:  Unknown
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 I get the very unhelpful "unable to list source for <exception thrown>". I
 would like to get one of the following two responses, the last one is
 best.
 {{{
 Do this and that to list source
 }}}
 {{{
 We currently cannot list source, because you did and that Do you still
 want to list source                although it requires to do that and
 that(for example automatically recompiling and reexecuting it until the
 same program point) [Y/n]?
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1826>
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