[GHC] #13073: BooleanFormula implies is wrong
#13073: BooleanFormula implies is wrong -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The current implementation looks like this: {{{ implies :: Eq a => BooleanFormula a -> BooleanFormula a -> Bool x `implies` Var y = x `impliesAtom` y x `implies` And ys = all (implies x . unLoc) ys x `implies` Or ys = any (implies x . unLoc) ys x `implies` Parens y = x `implies` (unLoc y) }}} This cannot possibly be correct: this will decompose the formula A \/ B -> A \/ B in the following way {{{ Or [Var a, Var b] `implies` Or [Var a, Var b] Or [Var a, Var b] `implies` Var a || Or [Var a, Var b] `implies` Var b }}} But neither of the decomposed formulas are true. I didn't find a case in the typechecker where this actually mattered. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13073 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13073: BooleanFormula implies is wrong -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): I am fairly sure the only place where `BooleanFormula` is used is `MINIMAL` pragmas but I assume you were trying to use it for something else if you found this bug. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13073#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13073: BooleanFormula implies is wrong -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2925 Wiki Page: | -------------------------------------+------------------------------------- Changes (by ezyang): * status: new => patch * differential: => Phab:D2925 Comment: Yes, implies is never used, only impliesAtom which seems to be implemented correctly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13073#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13073: BooleanFormula implies is wrong -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: patch Priority: normal | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2925 Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * milestone: => 8.2.1 @@ -21,1 +21,2 @@ - But neither of the decomposed formulas are true. + But neither of the decomposed formulas are true, so GHC will never find a + proof. New description: The current implementation looks like this: {{{ implies :: Eq a => BooleanFormula a -> BooleanFormula a -> Bool x `implies` Var y = x `impliesAtom` y x `implies` And ys = all (implies x . unLoc) ys x `implies` Or ys = any (implies x . unLoc) ys x `implies` Parens y = x `implies` (unLoc y) }}} This cannot possibly be correct: this will decompose the formula A \/ B -> A \/ B in the following way {{{ Or [Var a, Var b] `implies` Or [Var a, Var b] Or [Var a, Var b] `implies` Var a || Or [Var a, Var b] `implies` Var b }}} But neither of the decomposed formulas are true, so GHC will never find a proof. I didn't find a case in the typechecker where this actually mattered. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13073#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13073: BooleanFormula implies is wrong
-------------------------------------+-------------------------------------
Reporter: ezyang | Owner:
Type: bug | Status: patch
Priority: normal | Milestone: 8.2.1
Component: Compiler (Type | Version: 8.1
checker) |
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D2925
Wiki Page: |
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Comment (by Edward Z. Yang
#13073: BooleanFormula implies is wrong -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: closed Priority: normal | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.1 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2925 Wiki Page: | -------------------------------------+------------------------------------- Changes (by ezyang): * status: patch => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13073#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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