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[GHC] #6041: Program hangs when run under Ubuntu Precise

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[GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------+------------------------------------------------
 Reporter:  dsf            |          Owner:                  
     Type:  bug            |         Status:  new            
 Priority:  normal         |      Component:  Compiler        
  Version:  7.4.1          |       Keywords:                  
       Os:  Linux          |   Architecture:  Unknown/Multiple
  Failure:  Runtime crash  |       Testcase:                  
Blockedby:                 |       Blocking:                  
  Related:                 |  
---------------------------+------------------------------------------------
 This code hangs when running under Ubuntu Precise. However, it works in a
 Precise changeroot on an Ubuntu Lucid machine -- indicating it could be
 kernel specific.  My guess would be that it would succeed on a Precise
 machine running a Lucid kernel, but we have not tried that.

 Any of the following changes make the code work:

  1. replacing 'readTVar u' with 'return ()'
  2. removing the 'Wrapper' monad and just using 'StateT'
  3. deriving the 'MonadState' instance instead of righting it by hand
  4. copying the definition of 'modify' into the local module and use that
 instead of the imported version

 The final mystery: If the binary is built in a precise changeroot (where
 it works) and then copied to a precise machine ... it still works.  And if
 it is built on a real precise machine, where it fails, it still fails when
 copied to a precise changeroot on a lucid machine.

 So, there's that.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------+------------------------------------------------
 Reporter:  dsf            |          Owner:                  
     Type:  bug            |         Status:  new            
 Priority:  normal         |      Component:  Compiler        
  Version:  7.4.1          |       Keywords:                  
       Os:  Linux          |   Architecture:  Unknown/Multiple
  Failure:  Runtime crash  |       Testcase:                  
Blockedby:                 |       Blocking:                  
  Related:                 |  
---------------------------+------------------------------------------------
Changes (by JeremyShaw):

 * cc: JeremyShaw (added)


Comment:

 The tool chain for the real precise machine and the precise chroot were
 both installed by apt-get installing the same build of GHC. The
 environments should be nearly identical aside from things like the kernel,
 which are not affected by chroot.

 The fact that the code does not work in the real precise environment is
 mysterious on its own. Especially given the types of changes that make it
 work. However, we have seen that type of bug before. But, what makes this
 bug even more mysterious is the fact that some subtle aspect of the
 environment the compiler is running in is also significant. Though, it
 does seem like STM is needed to trigger the bug -- which could indicate
 that the RTS is involved? Some aspect that is effected by the environment
 the code is built in, rather than the environment it is run in?

 We could possibly provide ssh access to a machine that exhibits this bug
 if needed. We are currently only running precise on a laptop, so its
 availability is variable.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:1>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  infoneeded  
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by simonmar):

  * priority:  normal => high
  * difficulty:  => Unknown
  * status:  new => infoneeded
  * milestone:  => 7.4.2


Comment:

 Could you collect some more information for me:

  * Compile with `-debug`, run with `+RTS -Ds` (both a working and a
 failing run)
  * run under `strace` (both a working and a failing run)

 You didn't mention whether this was with `-threaded` or not.  Does that
 make a difference?

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:2>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  infoneeded  
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by dsf):

 Up until now we have been using the -threaded option, but I removed it for
 these tests and the behavior is the same.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:3>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  new          
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by simonmar):

  * status:  infoneeded => new


--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:4>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  new          
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by simonmar):

 Fascinating - the failing case enters a black hole and then exits with
 `<<loop>>`.  You said originally it was hanging, but the trace seems to
 show that it exited, is that right?

 Unfortunately I can't tell what black hole it has entered without
 debugging.  Could you set me up an SSH login?

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:5>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  new          
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by dsf):

 I believe it hangs when run from ghci and prints <<loop>> and exits when
 compiled.  I have set up an account simonmar/simonmar for you, ssh to
 foxthompson.dynalias.org.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:6>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  new          
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by dsf):

 (There's nothing interesting on that machine, in case you're all
 wondering!)

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:7>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  new          
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by cliffordbeshers):

 * cc: clifford.beshers@… (added)


--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:8>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  infoneeded  
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by simonmar):

  * status:  new => infoneeded


Comment:

 I can't seem to reproduce the bug.  Here's my session with the things I've
 tried:

 {{{
 simonmar@x220:~$ ghc Main.hs
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 simonmar@x220:~$ ./Main
 hello
 simonmar@x220:~$ uname -a
 Linux x220 3.2.0-23-generic #36-Ubuntu SMP Tue Apr 10 20:39:51 UTC 2012
 x86_64 x86_64 x86_64 GNU/Linux
 simonmar@x220:~$ ghci Main.hs
 GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 Ok, modules loaded: Main.
 Prelude Main> main
 Loading package transformers-0.3.0.0 ... linking ... done.
 Loading package mtl-2.1.1 ... linking ... done.
 Loading package array-0.4.0.0 ... linking ... done.
 Loading package stm-2.3 ... linking ... done.
 hello
 Prelude Main>
 Leaving GHCi.
 simonmar@x220:~$ ghc -O Main.hs
 simonmar@x220:~$ ghc -O Main.hs -fforce-recomp
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 simonmar@x220:~$ ./Main
 hello
 simonmar@x220:~$ ghc -O2 Main.hs -fforce-recomp
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 simonmar@x220:~$ ./Main
 hello
 simonmar@x220:~$ ghc -O2 -threaded Main.hs -fforce-recomp
 [1 of 1] Compiling Main             ( Main.hs, Main.o )
 Linking Main ...
 simonmar@x220:~$ ./Main
 hello
 }}}

 Could you try with the `simonmar` account on that machine and see if you
 can reproduce it?

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:9>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
---------------------------------+------------------------------------------
    Reporter:  dsf               |       Owner:              
        Type:  bug               |      Status:  infoneeded  
    Priority:  high              |   Milestone:  7.4.2        
   Component:  Compiler          |     Version:  7.4.1        
    Keywords:                    |          Os:  Linux        
Architecture:  Unknown/Multiple  |     Failure:  Runtime crash
  Difficulty:  Unknown           |    Testcase:              
   Blockedby:                    |    Blocking:              
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by dsf):

 Now I can't reproduce it anywhere.  I do have one binary that still
 exhibits the behavior, I've placed it in your home directory.

 I dist-upgraded the machine yesterday before I created your account.  I
 figured if this bug was caused by something in libc6 we would want to know
 that.  So that might have made it go away.  On the other hand, that should
 make it go away in the binary that is still exhibiting the bug.  Bad
 decision on my part?  Maybe.  I have been routinely dist-upgrading the
 precise install as we approached the final release.

 I could try reinstalling the beta iso if we want to pursue it, but if its
 caused by nastyness in libc I'm not sure its worth it.  Let me know if you
 want me to try this.  Otherwise I may not get to it for a few days.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:10>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  closed          
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:  worksforme     |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------
Changes (by simonmar):

  * status:  infoneeded => closed
  * resolution:  => worksforme


Comment:

 I looked into it a bit, and the binary seems to contain a top-level CAF of
 the form "x = x", which obviously causes a loop when evaluated.  It's not
 clear where this came from, and without being able to reproduce it I can't
 make any further progress.  Thanks for the report - if it happens again,
 please reopen the ticket.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:11>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  new            
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:                 |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------
Changes (by guest):

  * status:  closed => new
  * resolution:  worksforme =>


Comment:

 Hello

 I was very intrigued by this report, and hunted the bug for a long time,
 but it's very simple. It's not GHC.

 You did not define `state` for `Wrapper`. That's not bad, since the
 documentation in mtl-2.1 states that minimal definition is `get`/`put`.
 The default definition for `state` is:

 {{{
     state f = do
       s <- get
       let ~(a, s) = f s
       put s
       return a
 }}}

 but in transformers-0.3 you can find:

 {{{
 instance (Monad m) => Monad (StateT s m) where
     return a = state $ \s -> (a, s)
     [...]
 }}}

 so `state` and `return` are mutually calling themselves, and `state` in
 second code should be `StateT`. Bug in transformers. I reopened the ticket
 as I am unsure where to report this...

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:12>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  new            
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:                 |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------

Comment(by guest):

 On the other hand I undo my diagnosis - that `state` in transformers will
 evaluate to `StateT` monad, not `Wrapper`. In any case here is a simpler
 program giving <<loop>> on my machine:

 {{{
 {-# LANGUAGE FlexibleContexts, FlexibleInstances,
 GeneralizedNewtypeDeriving, MultiParamTypeClasses #-}
 module Main (main) where

 import Control.Monad.State    (MonadState, StateT, evalStateT, get, put,
 state)

 modify :: MonadState s m => (s -> s) -> m ()
 modify f = state (\s -> ((), f s))

 newtype Wrapper a = Wrapper { unWrapper :: StateT () IO a }
     deriving (Functor, Monad)

 instance MonadState () Wrapper where
   get   = Wrapper get
   put s = Wrapper (put s)
 --  state f = Wrapper (state f)  -- uncomment and it works

 setUnique :: Wrapper ()
 setUnique =
     do u <- get
        seq u $ return ()

 main :: IO ()
 main =
       do putStrLn "hello"
          evalStateT (unWrapper (modify id >> setUnique)) ()
 }}}

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:13>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  new            
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:                 |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------
Changes (by simonmar):

 * cc: ross (added)


Comment:

 Thanks for the diagnosis.

 Ross - please see the bug report against transformers above.  I'm closing
 this ticket here.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:14>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  closed          
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:  invalid        |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------
Changes (by simonmar):

  * status:  new => closed
  * resolution:  => invalid


--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:15>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  closed          
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:  invalid        |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------

Comment(by cliffordbeshers):

 The modified program provided by guest does not loop for me, using
 SeeReason's Ubuntu package environment where the bug was originally
 witnessed (albeit with the packages rebuilt many times since.)  ghc 7.4.1
 and transformers 0.3.

 Ross, if you make a new ticket, please drop a forwarding link here.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:16>
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Re: [GHC] #6041: Program hangs when run under Ubuntu Precise

GHC
In reply to this post by GHC
#6041: Program hangs when run under Ubuntu Precise
----------------------------+-----------------------------------------------
  Reporter:  dsf            |          Owner:                  
      Type:  bug            |         Status:  closed          
  Priority:  high           |      Milestone:  7.4.2          
 Component:  Compiler       |        Version:  7.4.1          
Resolution:  invalid        |       Keywords:                  
        Os:  Linux          |   Architecture:  Unknown/Multiple
   Failure:  Runtime crash  |     Difficulty:  Unknown        
  Testcase:                 |      Blockedby:                  
  Blocking:                 |        Related:                  
----------------------------+-----------------------------------------------

Comment(by guest):

 @cliffordbeshers: Does the original Main.hs given by dsf gives <<loop>> on
 your machine while my reduced version does not? That would be extremely
 strange and if so I would reopen the ticket. I can reproduce looping on
 both programs, with Ubuntu Precise, 3.2.0-25-generic-pae, GHC 7.4.1.

 I am pretty sure of my overall diagnosis. Please note that all fixes (1) -
 (4) given in initial bug report are connected to the state monad. The
 program puts infinite loop as a state with `modify id`, and then attempts
 to read it with `readTVar u`. For example, if you change `_ <- liftIO $
 atomically $ readTVar u` to `print $ seq u ()`, the behaviour is the same,
 indicating that TVars are not core of the issue and can be replaced with
 ().

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6041#comment:17>
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