Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  closed  
 
  Priority:  highest |  Milestone:  7.6.1   
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  fixed   |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--

Comment(by jwlato):

 I am happy to confirm that this is fixed for me with ghc-7.6.0.20120822.
 I think you meant the Hets issue in #7150; ticket #7050 appears unrelated.

 Anyway, thanks again for fixing this, I'm glad the test case was helpful.

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  closed  
 
  Priority:  highest |  Milestone:  7.6.1   
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  fixed   |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--
Changes (by simonpj):

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


Comment:

 Closing meanwhile, since we're all done here.

 This patch also should fix the same problem in Hets, #7050.

 Simon

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  new 
 
  Priority:  highest |  Milestone:  7.6.1   
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--
Changes (by simonpj):

  * milestone:  7.8.1 => 7.6.1


Comment:

 I think this is fixed by this HEAD patch, which I have now merged into
 7.6:
 {{{
 commit 702f0db0dd4e85de445e5edb5e6294057ebe6792
 Author: Simon Peyton Jones 
 Date:   Wed Aug 22 18:03:12 2012 +0100

 Numerous small changes to the constraint solver

 The main thing is that we now keep unsolved Derived constraints in
 the
 wc_flats of a WantedConstraints, rather than discarding them each
 time.
 This actually fixes a poential (admittedly obscure) bug, when we
 currently
 discard a superclass constraint, and may never re-generate it, and
 may
 thereby miss a functional dependency.

 Instead, reportErrors filters out Derived constraints that we
 don't want
 to report.

 The other changes are all small refactorings following our walk-
 through.

 MERGED from commit 9c0a6bbb0194f65cd62e48936c0c00fc4888eef3 on HEAD

  compiler/typecheck/TcErrors.lhs   |   53 +-
  compiler/typecheck/TcHsSyn.lhs|   50 --
  compiler/typecheck/TcInteract.lhs |  192
 +
  compiler/typecheck/TcRnTypes.lhs  |   42 
  compiler/typecheck/TcSMonad.lhs   |  137 +-
  compiler/typecheck/TcSimplify.lhs |   86 +
  6 files changed, 228 insertions(+), 332 deletions(-)
 }}}
 Can you try now with the 7.6 branch when the next snapshot appears?

 I'll add your example as a regression test (for HEAD).

 Simon

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  new 
 
  Priority:  highest |  Milestone:  7.8.1   
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--
Changes (by simonpj):

  * priority:  normal => highest
  * status:  closed => new
  * resolution:  fixed =>
  * milestone:  => 7.8.1


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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  closed  
 
  Priority:  normal  |  Milestone:  
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  fixed   |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--

Comment(by simonpj):

 That is very strange.  The patches I ''thought'' were important have been
 merged. I'll build 7.6 and try wit that.  It's great to have your small
 test case, thank you.

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  closed  
 
  Priority:  normal  |  Milestone:  
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  fixed   |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--

Comment(by jwlato):

 I can confirm my problem is fixed in HEAD, but not ghc-7.6.0.20120820.
 Hopefully it'll be merged soon.  Thanks for looking at this so quickly!

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
-+--
  Reporter:  jwlato  |  Owner:  
 
  Type:  bug | Status:  closed  
 
  Priority:  normal  |  Milestone:  
 
 Component:  Compiler (Type checker) |Version:  7.6.1-rc1   
 
Resolution:  fixed   |   Keywords:  type classes, 
fundeps
Os:  Unknown/Multiple|   Architecture:  
Unknown/Multiple 
   Failure:  GHC rejects valid program   | Difficulty:  Unknown 
 
  Testcase:  typecheck/should_compile/T7171  |  Blockedby:  
 
  Blocking:  |Related:  
 
-+--
Changes (by simonpj):

  * status:  new => closed
  * testcase:  => typecheck/should_compile/T7171
  * resolution:  => fixed


Comment:

 Re-open if you think this is still broken.

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Re: [GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
+---
Reporter:  jwlato   |   Owner:  
 
Type:  bug  |  Status:  new 
 
Priority:  normal   |   Milestone:  
 
   Component:  Compiler (Type checker)  | Version:  7.6.1-rc1   
 
Keywords:  type classes, fundeps|  Os:  Unknown/Multiple
 
Architecture:  Unknown/Multiple | Failure:  GHC rejects valid 
program
  Difficulty:  Unknown  |Testcase:  
 
   Blockedby:   |Blocking:  
 
 Related:   |  
+---
Changes (by simonpj):

  * difficulty:  => Unknown


Comment:

 Thanks. Happily I believe this is already fixed -- at least your test case
 works for me; I think the fix was the one for #7128.  And the symptoms
 look very much like #7150, which also works now.

 If you can try with HEAD that'd be great.

 Simon

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[GHC] #7171: erroneous overlapping instances reported with FunDeps

[GHC]

#7171: erroneous overlapping instances reported with FunDeps
---+
 Reporter:  jwlato |  Owner:
 
 Type:  bug| Status:  new   
 
 Priority:  normal |  Component:  Compiler (Type 
checker)
  Version:  7.6.1-rc1  |   Keywords:  type classes, fundeps 
 
   Os:  Unknown/Multiple   |   Architecture:  Unknown/Multiple  
 
  Failure:  GHC rejects valid program  |   Testcase:
 
Blockedby: |   Blocking:
 
  Related: |  
---+
 When a superclass constraint has functional dependencies, in certain cases
 GHC-7.6 erroneously reports that duplicate instances are found.

 file Foo.hs
 {{{
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE FlexibleInstances #-}

 module Foo where

 import Data.ByteString as B
 import Data.Word

 class Foo a b | a -> b

 class (Foo a b) => Bar a b | a -> b

 instance Foo [a] a
 instance Bar [a] a
 instance Foo ByteString Word8
 instance Bar ByteString Word8

 test :: Bar full item => full -> full
 test inp = inp

 -- this works
 -- _test_x :: ByteString -> ByteString
 -- _test_x = test


 }}}

 file Main.hs
 {{{
 module Main where

 import Foo
 import Data.ByteString

 -- this works
 -- test1 :: [Int] -> [Int]
 -- test1 = test

 -- this fails
 test2 :: ByteString -> ByteString
 test2 = test

 }}}

 ghc reports

 {{{
 Main.hs:12:9:
 Overlapping instances for Foo ByteString GHC.Word.Word8
   arising from a use of `test'
 Matching instances:
   instance Foo ByteString GHC.Word.Word8 -- Defined at Foo.hs:20:10
 There exists a (perhaps superclass) match:
 (The choice depends on the instantiation of `'
  To pick the first instance above, use -XIncoherentInstances
  when compiling the other instance declarations)
 In the expression: test
 In an equation for `test2': test2 = test
 }}}

 For this to manifest, I think that at least the following must be true:
   - a function with class constraints must be called from a separate
 module
   - the type class instance must be monomorphic in the fundep-to parameter

 This example works in ghc-7.4.2.

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