#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