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[GHC] #6060: the 'impossible' happened

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[GHC] #6060: the 'impossible' happened

GHC
#6060: the 'impossible' happened
------------------------------+---------------------------------------------
 Reporter:  lerkok            |          Owner:                  
     Type:  bug               |         Status:  new            
 Priority:  normal            |      Component:  Compiler        
  Version:  7.4.1             |       Keywords:                  
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
  Failure:  None/Unknown      |       Testcase:                  
Blockedby:                    |       Blocking:                  
  Related:                    |  
------------------------------+---------------------------------------------
 {{{
 $ cat bug.hs
 foo = do let bad = [True | x <- [] | y <- []]
 $ ghc bug.hs
 [1 of 1] Compiling Main             ( bug.hs, bug.o )

 bug.hs:1:10:ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.1 for x86_64-apple-darwin):
         Prelude.undefined
 }}}

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6060>
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Re: [GHC] #6060: the 'impossible' happened

GHC
#6060: the 'impossible' happened
---------------------------------+------------------------------------------
    Reporter:  lerkok            |       Owner:                    
        Type:  bug               |      Status:  new              
    Priority:  normal            |   Milestone:  7.6.1            
   Component:  Compiler          |     Version:  7.4.1            
    Keywords:                    |          Os:  Unknown/Multiple  
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
  Difficulty:  Unknown           |    Testcase:                    
   Blockedby:                    |    Blocking:                    
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by pcapriotti):

  * difficulty:  => Unknown
  * milestone:  => 7.6.1
  * failure:  None/Unknown => Compile-time crash


Comment:

 Thanks for the report.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6060#comment:1>
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Re: [GHC] #6060: the 'impossible' happened

GHC
In reply to this post by GHC
#6060: the 'impossible' happened
---------------------------------+------------------------------------------
    Reporter:  lerkok            |       Owner:                    
        Type:  bug               |      Status:  patch            
    Priority:  normal            |   Milestone:  7.6.1            
   Component:  Compiler          |     Version:  7.4.1            
    Keywords:                    |          Os:  Unknown/Multiple  
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
  Difficulty:  Unknown           |    Testcase:                    
   Blockedby:                    |    Blocking:                    
     Related:                    |  
---------------------------------+------------------------------------------
Changes (by pcapriotti):

  * status:  new => patch


Comment:

 The pretty printer for parallel comprehensions is broken. Attached patch
 and testcase.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6060#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler

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Re: [GHC] #6060: the 'impossible' happened

GHC
In reply to this post by GHC
#6060: the 'impossible' happened
---------------------------------+------------------------------------------
    Reporter:  lerkok            |       Owner:                    
        Type:  bug               |      Status:  patch            
    Priority:  normal            |   Milestone:  7.6.1            
   Component:  Compiler          |     Version:  7.4.1            
    Keywords:                    |          Os:  Unknown/Multiple  
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
  Difficulty:  Unknown           |    Testcase:                    
   Blockedby:                    |    Blocking:                    
     Related:                    |  
---------------------------------+------------------------------------------

Comment(by simonpj@…):

 commit 67c793a3a13482bc897810e3b5e13f96942afc68
 {{{
 Author: Simon Peyton Jones <[hidden email]>
 Date:   Tue May 1 08:07:52 2012 +0100

     Tidy up a remaining glitch in unification

     There was one place, in type checking parallel list comprehensions
     where we were unifying types, but had no convenient way to use the
     resulting coercion; instead we just checked that it was Refl.  This
     was Wrong Wrong; it might fail unpredicably in a GADT-like situation,
     and it led to extra error-generation code used only in this one place.

     This patch tidies it all up, by moving the 'return' method from the
     *comprehension* to the ParStmtBlock. The latter is a new data type,
     now used for each sub-chunk of a parallel list comprehension.

     Because of the data type change, quite a few modules are touched,
     but only in a fairly trivial way. The real changes are in TcMatches
     (and corresponding desugaring); plus deleting code from TcUnify.

     This patch also fixes the pretty-printing bug in Trac #6060

  compiler/deSugar/Coverage.lhs    |   14 ++++----
  compiler/deSugar/DsArrows.lhs    |    4 +-
  compiler/deSugar/DsListComp.lhs  |   39 ++++++++++-----------
  compiler/hsSyn/Convert.lhs       |    4 +-
  compiler/hsSyn/HsExpr.lhs        |   33 ++++++++++++------
  compiler/hsSyn/HsUtils.lhs       |   12 +++---
  compiler/main/HscMain.hs         |    4 +-
  compiler/parser/Parser.y.pp      |    3 +-
  compiler/rename/RnExpr.lhs       |   29 +++++++--------
  compiler/typecheck/TcErrors.lhs  |    8 ----
  compiler/typecheck/TcHsSyn.lhs   |   23 ++++++------
  compiler/typecheck/TcMatches.lhs |   70
 ++++++++++----------------------------
  compiler/typecheck/TcUnify.lhs   |   11 ------
  13 files changed, 104 insertions(+), 150 deletions(-)
 }}}

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6060#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler

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Re: [GHC] #6060: the 'impossible' happened

GHC
In reply to this post by GHC
#6060: the 'impossible' happened
---------------------------------------+------------------------------------
  Reporter:  lerkok                    |          Owner:                  
      Type:  bug                       |         Status:  closed          
  Priority:  normal                    |      Milestone:  7.6.1          
 Component:  Compiler                  |        Version:  7.4.1          
Resolution:  fixed                     |       Keywords:                  
        Os:  Unknown/Multiple          |   Architecture:  Unknown/Multiple
   Failure:  Compile-time crash        |     Difficulty:  Unknown        
  Testcase:  rename/should_fail/T6060  |      Blockedby:                  
  Blocking:                            |        Related:                  
---------------------------------------+------------------------------------
Changes (by simonpj):

  * status:  patch => closed
  * testcase:  => rename/should_fail/T6060
  * resolution:  => fixed


Comment:

 Thanks. Coincidentally I found an old patch I've been meaning to commit
 for ages, that overlapped, so I combined them.

 Simon

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6060#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler

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