#10326: ImpredicativeTypes: Unable to use in Functor etc.. -------------------------------------+------------------------------------- Reporter: j80JjBjVNRMajmA | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: wontfix | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * status: new => closed * resolution: => wontfix Comment: `ImpredicativeTypes` is thoroughly broken and is unsupported. In the past, this extension was more properly implemented, but caused more grief than help even then. If you want this kind of thing, use a `newtype` instead of a `type`. It's surely more annoying, but it's better to have an annoying option instead of a totally-broken one. There are a number of Very Clever People working on integrating impredicativity with GHC-style type inference. (I'm not one of them, however.) In GHC's view, there has not yet been the right solution. We all look forward to when the right solution is found! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10326#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler