#10082: Church Booleans - xor -------------------------------------+------------------------------------- Reporter: honza889 | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.9 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Incorrect result | (amd64) at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => invalid Comment: You are trying to use higher rank types here, so you need type signatures. (See [http://research.microsoft.com/en-us/um/people/simonpj/papers/higher- rank/index.htm Practical type inference for higher rank types]). This works: {{{ {-# LANGUAGE RankNTypes #-} module T10082 where type CBool = forall a. a->a->a lTrue :: CBool lTrue = \x y -> x lFalse :: CBool lFalse = \x y -> y lNot :: CBool -> CBool lNot = \t -> t lFalse lTrue lXor :: CBool -> CBool -> CBool lXor = \u v -> u (lNot v) (lNot (lNot v)) -- You omitted some parens here! lXor' :: CBool -> CBool -> CBool lXor' = \u v -> u (v lFalse lTrue) (v lTrue lFalse) lXor'' :: CBool -> CBool -> CBool lXor'' = \u v -> u (lNot v) (v) lXor''' :: CBool -> CBool -> CBool lXor''' = \u v -> u (lNot v) v }}} So it all seems fine to me. I'll close as invalid but do re-open if you disagree. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10082#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler