[GHC] #5751: code works in 7.0 but hangs in 7.2/7.4 due to changes in type checker (most likely)

[GHC]

#5751: code works in 7.0 but hangs in 7.2/7.4 due to changes in type checker (most
likely)
-------------------------------+--------------------------------------------
    Reporter:  JeremyShaw      |       Owner:                             
        Type:  bug             |      Status:  new                        
    Priority:  normal          |   Milestone:                             
   Component:  Compiler        |     Version:  7.2.1                      
    Keywords:                  |          Os:  Linux                      
Architecture:  x86_64 (amd64)  |     Failure:  Incorrect result at runtime
  Difficulty:  Unknown         |    Testcase:                             
   Blockedby:                  |    Blocking:                             
     Related:                  |  
-------------------------------+--------------------------------------------

Comment(by JeremyShaw):

 I have attached a test case.

 As submitted, the test case works under 7.0.4 and 7.2.2 and fails under
 7.4rc1 and 7.5.20111215.

 When successful, the application will print 'done.' and exit. When it
 fails the application will hang or print <<loop>>.

 if you uncomment line 22

 {{{
 -- instance Widgets (IdentityT IO) -- if you uncomment this, it will work
 }}}

 The code will work 7.4rc1 (and probably 7.5).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5751#comment:3>
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