Re: [GHC] #7525: Compiler panic with ill-typed code using implicit parameters

[GHC]

#7525: Compiler panic with ill-typed code using implicit parameters
--+-
  Reporter:  parcs|  Owner:  
  Type:  bug  | Status:  closed  
  Priority:  normal   |  Milestone:  
 Component:  Compiler |Version:  7.7 
Resolution:  fixed|   Keywords:  
Os:  Unknown/Multiple |   Architecture:  Unknown/Multiple
   Failure:  Compile-time crash   | Difficulty:  Unknown 
  Testcase:  typecheck/should_fail/T7525  |  Blockedby:  
  Blocking:   |Related:  
--+-
Changes (by igloo):

  * status:  merge => closed
  * resolution:  => fixed


Comment:

 Already works in 7.6 branch, so not merging.

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Re: [GHC] #7525: Compiler panic with ill-typed code using implicit parameters

[GHC]

#7525: Compiler panic with ill-typed code using implicit parameters
-+--
Reporter:  parcs |   Owner: 
Type:  bug   |  Status:  merge  
Priority:  normal|   Milestone: 
   Component:  Compiler  | Version:  7.7
Keywords:|  Os:  Unknown/Multiple   
Architecture:  Unknown/Multiple  | Failure:  Compile-time crash 
  Difficulty:  Unknown   |Testcase:  typecheck/should_fail/T7525
   Blockedby:|Blocking: 
 Related:|  
-+--
Changes (by simonpj):

  * status:  new => merge
  * difficulty:  => Unknown
  * testcase:  => typecheck/should_fail/T7525


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Re: [GHC] #7525: Compiler panic with ill-typed code using implicit parameters

[GHC]

#7525: Compiler panic with ill-typed code using implicit parameters
---+
Reporter:  parcs   |  Owner:  
Type:  bug | Status:  new 
Priority:  normal  |  Component:  Compiler
 Version:  7.7 |   Keywords:  
  Os:  Unknown/Multiple|   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |  Blockedby:  
Blocking:  |Related:  
---+

Comment(by simonpj@…):

 commit 1d07cc04ebcaa2df69824aeb1406557946e6dd19
 {{{
 Author: Simon Peyton Jones 
 Date:   Mon Dec 24 09:46:55 2012 +

 Remember to zonk when taking free variables in simpl_top

 Forgetting this meant that we were upating the same
 meta-tyvar twice.  Fixes Trac #7525.

  compiler/typecheck/TcSMonad.lhs   |4 
  compiler/typecheck/TcSimplify.lhs |   24 
  2 files changed, 16 insertions(+), 12 deletions(-)
 }}}

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Re: [GHC] #7525: Compiler panic with ill-typed code using implicit parameters

[GHC]

#7525: Compiler panic with ill-typed code using implicit parameters
---+
Reporter:  parcs   |  Owner:  
Type:  bug | Status:  new 
Priority:  normal  |  Component:  Compiler
 Version:  7.7 |   Keywords:  
  Os:  Unknown/Multiple|   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |  Blockedby:  
Blocking:  |Related:  
---+

Comment(by parcs):

 On second thought, this is probably an easier snippet to debug (I can't
 edit the description of the ticket for some reason):

 {{{
 {-# LANGUAGE ImplicitParams #-}
 module Bug where

 hmm :: ()
 hmm = let ?a = True in ?a
 }}}

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[GHC] #7525: Compiler panic with ill-typed code using implicit parameters

[GHC]

#7525: Compiler panic with ill-typed code using implicit parameters
---+
Reporter:  parcs   |  Owner:  
Type:  bug | Status:  new 
Priority:  normal  |  Component:  Compiler
 Version:  7.7 |   Keywords:  
  Os:  Unknown/Multiple|   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |  Blockedby:  
Blocking:  |Related:  
---+
 The following snippet produces a compiler panic with GHC 7.7.20121221:

 {{{
 {-# LANGUAGE ImplicitParams #-}

 hmm :: ()
 hmm = let ?a = True in ?a

 main = print hmm
 }}}

 Which results in the error message:

 {{{
 [1 of 1] Compiling Main ( bug.hs, bug.o )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.7.20121221 for x86_64-unknown-linux):
 ASSERT failed!
 file compiler/typecheck/TcMType.lhs line 407
 Double update of meta tyvar
   t_ajp{tv} [tau[0]]
   Indirect ghc-prim:GHC.Types.Bool{(w) tc 3c}

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 Note that the same snippet compiled with GHC 7.6.1 doesn't panic, and
 instead gives a type error:

 {{{
 [1 of 1] Compiling Main ( bug.hs, bug.o )

 bug.hs:4:24:
 Couldn't match type `Bool' with `()'
 When using functional dependencies to combine
   ?a::Bool,
 arising from the implicit-parameter bindings for ?a
 at bug.hs:4:7-25
   ?a::(),
 arising from a use of implicit parameter `?a' at bug.hs:4:24-25
 In the expression: ?a
 In the expression: let ?a = True in ?a
 }}}

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