Re: [GHC] #7541: Unavoidable duplicate constraint warning

2013-01-02 Thread GHC 
#7541: Unavoidable duplicate constraint warning
--+-
Reporter:  blamario   |  Owner: 
 
Type:  bug| Status:  new
 
Priority:  normal |  Component:  Compiler   
 
 Version:  7.6.1  |   Keywords: 
 
  Os:  Unknown/Multiple   |   Architecture:  
Unknown/Multiple
 Failure:  Incorrect warning at compile-time  |  Blockedby: 
 
Blocking: |Related: 
 
--+-

Comment(by simonpj@…):

 commit 5a6a223f855538112ec9d089425e34853fb3542b
 {{{
 Author: Simon Peyton Jones simo...@microsoft.com
 Date:   Wed Jan 2 11:57:00 2013 +

 Add flag -fwarn-duplicate-constraints

 This fixes Trac #7541, and is on by default.
 Use -fno-warn-duplicate-constraints to switch it off.

  compiler/main/DynFlags.hs  |5 -
  compiler/typecheck/TcMType.lhs |9 +
  docs/users_guide/flags.xml |7 +++
  docs/users_guide/using.xml |   19 +++
  4 files changed, 35 insertions(+), 5 deletions(-)
 }}}

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7541#comment:1
GHC http://www.haskell.org/ghc/
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Re: [GHC] #7541: Unavoidable duplicate constraint warning

2013-01-02 Thread GHC 
#7541: Unavoidable duplicate constraint warning
+---
  Reporter:  blamario   |  Owner:   
   
  Type:  bug| Status:  closed   
   
  Priority:  normal |  Milestone:   
   
 Component:  Compiler   |Version:  7.6.1
   
Resolution:  fixed  |   Keywords:   
   
Os:  Unknown/Multiple   |   Architecture:  
Unknown/Multiple
   Failure:  Incorrect warning at compile-time  | Difficulty:  Unknown  
   
  Testcase:  typecheck/should_compile/T7541 |  Blockedby:   
   
  Blocking: |Related:   
   
+---
Changes (by simonpj):

  * status:  new = closed
  * difficulty:  = Unknown
  * resolution:  = fixed
  * testcase:  = typecheck/should_compile/T7541


Comment:

 OK I've added a flag to suppress duplicate constraint warnings.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7541#comment:2
GHC http://www.haskell.org/ghc/
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[GHC] #7541: Unavoidable duplicate constraint warning

2013-01-01 Thread GHC 
#7541: Unavoidable duplicate constraint warning
--+-
Reporter:  blamario   |  Owner: 
 
Type:  bug| Status:  new
 
Priority:  normal |  Component:  Compiler   
 
 Version:  7.6.1  |   Keywords: 
 
  Os:  Unknown/Multiple   |   Architecture:  
Unknown/Multiple
 Failure:  Incorrect warning at compile-time  |  Blockedby: 
 
Blocking: |Related: 
 
--+-
 The duplicate constraint warning can be triggered in a context where
 it's impossible to remove it, because the constraints come with a type
 synonym.

 The following standalone little module reproduces the problem:

 {{{
 {-# LANGUAGE FlexibleContexts, Rank2Types #-}

 module Test where

 type Constrained x y r = (Eq x, Eq y) = x - y - r

 f :: Constrained String String ()
 f = undefined
 }}}

 The warning is

 {{{
 Test.hs:7:6: Warning:
 Duplicate constraint(s): Eq String
 In the type signature for `f': f :: Constrained String String ()
 }}}

 The warning is present in 7.4.1 and 7.6.1, and presumably in the versions
 between as well.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7541
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler

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