[GHC] #10176: Invalid core generated with GHC 7.10 RC3

[GHC]

#10176: Invalid core generated with GHC 7.10 RC3
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        Reporter:  NeilMitchell      |                   Owner:
            Type:  bug               |                  Status:  patch
        Priority:  high              |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.10.1-rc3
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by NeilMitchell):

 To assess what does happen in this error case, I augmented the code to be:

 {{{
 buggy fun unit bool =
     runReaderT (do
         if bool then liftReaderT $ print () else pure ()
         if fun unit then do error2Args unit unit; liftReaderT $ print
 "here2" else pure ()
         ) () :: IO ()
 }}}

 Running {{{do print "here1"; buggy (const True) () True; print "here3"}}}
 gives {{{here1; here3}}}. GHC has used the presence of error to remove the
 {{{here2}}}, but since the code just falls out of the end of the function
 it returns back and still prints {{{here3}}}. That's a nasty result, and
 pretty much describes what happens in the full test case (I'm in the
 middle of compiling, and then suddenly I stop and do the thing that comes
 after compiling).

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10176#comment:17>
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