#11319: ImpredicativeTypes even more broken than usual -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.11 checker) | Keywords: Resolution: | ImpredicativeTypes Operating System: Linux | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * cc: a.serranomena@… (added) Comment: This is definitely fallout from Visible Type Application. The program in comment:3 typechecks fine without `ImpredicativeTypes` (indeed it does in Haskell 98!) and surely `ImpredicativeTypes` should be a conservative extension. But let's not invest much in "fixing" `ImpredicativeTypes` which is simply not supported at the moment. Alejandro Serrano (cc'd) is working on impredicativity right now, so I've added him to the cc list. Alejandro, what are you doing will be significantly affected by the "lazy instantiation" approach of Visible Type Application ([https://www.cis.upenn.edu/~eir/pubs.html see paper]), so you might want to look carefully. VTA is in GHC now! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11319#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler