Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
---+
  Reporter:  nobody|  Owner:  
  Type:  bug   | Status:  closed  
  Priority:  lowest|  Milestone:  _|_ 
 Component:  Compiler  |Version:  5.02
Resolution:  invalid   |   Keywords:  
Difficulty:  Unknown   | Os:  Unknown/Multiple
  Testcase:|   Architecture:  Unknown/Multiple
   Failure:  None/Unknown  |  
---+
Changes (by ganesh):

  * status:  new => closed
  * resolution:  None => invalid

Comment:

 Closing this with the approval of the GHC team
 (http://www.haskell.org/pipermail/glasgow-haskell-
 users/2009-November/018017.html)

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Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
---+
  Reporter:  nobody|  Owner:  
  Type:  bug   | Status:  new 
  Priority:  lowest|  Milestone:  _|_ 
 Component:  Compiler  |Version:  5.02
Resolution:  None  |   Keywords:  
Difficulty:  Unknown   | Os:  Unknown/Multiple
  Testcase:|   Architecture:  Unknown/Multiple
   Failure:  None/Unknown  |  
---+
Changes (by ganesh):

  * failure:  => None/Unknown

Comment:

 This is an unsolvable issue. Consider this simplified example:
 {{{
 foo x | x == 0 = 0
   | x /= 0 = 0
 }}}
 For "correct" Eq implementations these patterns are indeed exhaustive. But
 (a) GHC has no evidence that all Eq implementations are "correct", and (b)
 in general it would be undecidable to check whether arbitrary guards are
 exhaustive or not.

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Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
-+--
Reporter:  nobody|Owner:  
Type:  bug   |   Status:  new 
Priority:  lowest|Milestone:  _|_ 
   Component:  Compiler  |  Version:  5.02
Severity:  normal|   Resolution:  None
Keywords:|   Difficulty:  Unknown 
Testcase:|   Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |  
-+--
Changes (by igloo):

  * status:  assigned => new
  * owner:  nobody =>

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Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
-+--
Reporter:  nobody|Owner:  nobody  
Type:  bug   |   Status:  assigned
Priority:  lowest|Milestone:  _|_ 
   Component:  Compiler  |  Version:  5.02
Severity:  normal|   Resolution:  None
Keywords:|   Difficulty:  Unknown 
  Os:  Unknown   | Testcase:  
Architecture:  Unknown   |  
-+--
Comment (by simonmar):

 See #595

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Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
-+--
Reporter:  nobody|Owner:  nobody  
Type:  bug   |   Status:  assigned
Priority:  lowest|Milestone:  _|_ 
   Component:  Compiler  |  Version:  5.02
Severity:  normal|   Resolution:  None
Keywords:|   Difficulty:  Unknown 
  Os:  Unknown   | Testcase:  
Architecture:  Unknown   |  
-+--
Changes (by simonmar):

  * testcase:  =>

Comment:

 See also #1307

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Re: [GHC] #29: Check for exhaustive patterns is broken

[GHC]

#29: Check for exhaustive patterns is broken
---+
  Reporter:  nobody|  Owner:  nobody  
  Type:  bug   | Status:  assigned
  Priority:  lowest|  Milestone:  _|_ 
 Component:  Compiler  |Version:  5.02
  Severity:  normal| Resolution:  None
  Keywords:| Os:  Unknown 
Difficulty:  Unknown   |   Architecture:  Unknown 
---+
Changes (by igloo):

  * architecture:  => Unknown
  * difficulty:  => Unknown
  * milestone:  => _|_
  * os:  => Unknown

Old description:

> {{{
> When some of the patterns in a function definition or
> case expression contain guards, the compiler gives
> false warnings about non-exhaustive pattern matches.  A
> pity, because this kind of warning is very useful
> indeed!
>
> For example, I get
>  >ghc --make -Wall See.hs
>  ghc-5.02.1: chasing modules from: See.hs
>  Compiling See  ( See.hs, ./See.o )
>
>  See.hs:17: Warning: Pattern match(es) are
> non-exhaustive
>  In the definition of `insert':
> Patterns not matched: _ _ (TREE _ _ _ _)
>
>  See.hs:41: Warning: Pattern match(es) are
> non-exhaustive
> In a case alternative EMPTY: Patterns not matched:
> TREE _ _ _ _
>
> for the attached file.
>
> [I am not sure filling in the e-mail address box had
> any effect on the last two complaints I submitted, so I
> repeat my address here:
> [EMAIL PROTECTED]
> }}}

New description:

 {{{
 When some of the patterns in a function definition or
 case expression contain guards, the compiler gives
 false warnings about non-exhaustive pattern matches.  A
 pity, because this kind of warning is very useful
 indeed!

 For example, I get
  >ghc --make -Wall See.hs
  ghc-5.02.1: chasing modules from: See.hs
  Compiling See  ( See.hs, ./See.o )

  See.hs:17: Warning: Pattern match(es) are
 non-exhaustive
  In the definition of `insert':
 Patterns not matched: _ _ (TREE _ _ _ _)

  See.hs:41: Warning: Pattern match(es) are
 non-exhaustive
 In a case alternative EMPTY: Patterns not matched:
 TREE _ _ _ _

 for the attached file.

 [I am not sure filling in the e-mail address box had
 any effect on the last two complaints I submitted, so I
 repeat my address here:
 [EMAIL PROTECTED]
 }}}

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