[GHC] #7150: unjustified overlapping instances error

[GHC]

#7150: unjustified overlapping instances error
-------------------------+--------------------------------------------------
    Reporter:  maeder    |       Owner:                           
        Type:  bug       |      Status:  new                      
    Priority:  highest   |   Milestone:  7.6.1                    
   Component:  Compiler  |     Version:  7.6.1-rc1                
    Keywords:            |          Os:  Solaris                  
Architecture:  x86       |     Failure:  GHC rejects valid program
  Difficulty:  Unknown   |    Testcase:                           
   Blockedby:            |    Blocking:                           
     Related:            |  
-------------------------+--------------------------------------------------

Comment(by simonpj):

 OK that helped.  I had a similar error in `Static/AnalysisLibrary` which I
 fixed with an error thunk thus:
 {{{
   let mt = error "urk"
 --  mt <- if checkUri file then return noTime
 --    else lift $ getModificationTime file
 }}}
 But then everything compiled.  No overlapping instance error.  Now what?

 Simon
 {{{
 ...
 [492 of 502] Compiling Static.AnalysisLibrary ( Static/AnalysisLibrary.hs,
 Static/AnalysisLibrary.o )
 [493 of 502] Compiling Driver.AnaLib    ( Driver/AnaLib.hs,
 Driver/AnaLib.o )
 [494 of 502] Compiling CMDL.DgCommands  ( CMDL/DgCommands.hs,
 CMDL/DgCommands.o )
 [495 of 502] Compiling CMDL.ProveCommands ( CMDL/ProveCommands.hs,
 CMDL/ProveCommands.o )
 [496 of 502] Compiling CMDL.ConsCommands ( CMDL/ConsCommands.hs,
 CMDL/ConsCommands.o )
 [497 of 502] Compiling CMDL.Commands    ( CMDL/Commands.hs,
 CMDL/Commands.o )
 [498 of 502] Compiling CMDL.ParseProofScript ( CMDL/ParseProofScript.hs,
 CMDL/ParseProofScript.o )
 [499 of 502] Compiling CMDL.ProcessScript ( CMDL/ProcessScript.hs,
 CMDL/ProcessScript.o )
 [500 of 502] Compiling CMDL.Interface   ( CMDL/Interface.hs,
 CMDL/Interface.o )
 [501 of 502] Compiling PGIP.XMLparsing  ( PGIP/XMLparsing.hs,
 PGIP/XMLparsing.o )
 [502 of 502] Compiling Main             ( hets.hs, hets.o )
 Linking hets ...
 simonpj at cam-05-unx:~/tmp/Hets$
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7150#comment:13>
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